delivered the opinion of the Court.
In this products liability suit brought on a warranty theory, the dispositive question is whether the evidence was sufficient to present a jury issue as to the defendants’ liability.
In December of 1977, plaintiff A. Dwight Doggett purchased from defendant Farmers Service Company, located in Smithfield, a quantity of bagged cattle feed supplement known as “Pro-Blend 50,” to be used in his commercial farming operation in Isle of Wight County. The Pro-Blend 50, a protein staple containing processed grain by-products as well as dicalcium phosphates, was manufactured by defendant Southern States Cooperative, Incorporated, at its plant in Richmond. On January 9, 1978, after the feed supplement had been consumed by plaintiff’s cattle, 66 head died and a substantial number of additional head became violently ill from a poison sold, under the trade name of “Thimet.”
The poison, an organic phosphate, generically known as “phorate,” was manufactured by “American Cyanamid,” according to the evidence. Thimet is an extremely toxic compound having a strong and offensive odor, and is “widely used by farmers generally” as an insecticide and for rodent control.
In March of 1978, Doggett filed this suit against the retailer and manufacturer of Pro-Blend 50 seeking damages for the death and illness of the cattle. The plaintiff alleged that as the “direct result” of the poison being in the product, defendants had “breached the implied warranties of merchantability and fitness for the general and particular purposes for which plaintiff intended said cattle feed to be used.”
Following a March 1979 trial, the jury found in favor of the plaintiff against both defendants in the amount of $24,135. The trial court, overruling defendants’ post-trial motions, entered judgment on the verdict. We granted defendants appeals from the May 1979 final order.
According to settled, elementary rules of appellate procedure, we will recite the facts in the light most favorable to the plaintiff, *653who is before us armed with a jury verdict approved by the trial judge.
Preparation at the farm of the food given to plaintiffs cattle on Monday, January 9, began on the preceding Saturday, January 7. At the time, plaintiffs cattle were being fed a mixture of corn, Pro-Blend 50, and peanut vines.
After having fed the cattle on that Saturday, plaintiffs son, A. Dwight Doggett, Jr., a 30-year-old college graduate who had been a farmer for eight years, prepared for the Monday feeding. On Saturday, the son placed 3000 pounds of corn in the mixing tank of an empty portable feeding mill having a capacity of 6000 pounds. The corn, stored in large, enclosed metal corn bins located adjacent to plaintiffs house, was brought to the mill by an auger conveyor extending from the bin to the mill.
After loading the corn, the son moved the mill, using a tractor, to a position adjacent to the corn bins and in front of a small barn where the Pro-Blend 50 was stored. The feed supplement had been stowed by plaintiff in the same condition as received from the retailer. The Pro-Blend 50 was sold by Southern States in sealed, 100-pound bags made of woven “plastic” cloth, technically described by the bag manufacturer as “woven polypropylene ribbon,” an oil-based product. The supplement in question was from a quantity picked up by the retailer in November and December 1977 from the manufacturer and, in turn, obtained by the plaintiff from the retailer during the latter month.
Standing outside the barn door with his feet on the ground, the son reached into the barn, opened two sealed bags of Pro-Blend 50, and manually poured the contents into the “rear auger” or rear “hopper” of the feed mill. He smelled no Thimet, although he was familiar with its odor. The empty bags were left on the barn floor along with other empty bags from prior feedings.
The son then pulled the feed mill to an open shelter located near the plaintiffs house where the mill remained until early the following Monday when the feeding process was resumed. According to the evidence, the mill was not “tampered with” from Saturday to Monday, and there was no indication “directly or indirectly that anybody had introduced anything in the feed mill” during that period.
Near 7:30 a.m. on Monday, the son moved the mill from the shelter to another barn located about one-half mile from plaintiffs house where peanut vines, baled on plaintiffs farm during the pre*654vious Fall, were stored. Using a conveyor belt, the son completed filling the mixing tank of the mill, using about 20 bales of vines. The components of the mill were mixed and about 80 percent of the mixture was placed by the son in a feeder located about one-half mile from the vine barn and one mile from plaintiffs home. The mixture was “augered” from the mixing tank directly into the feeder. After placing the remainder of the food into a second feeder, the son pulled the empty mill back to the corn bins where the Saturday procedure was repeated and the mill with a mixture of corn and supplement again was parked under the shelter.
During Monday afternoon, plaintiff noticed a number of cattle in distress and some dying. Doggett and his son immediately “[ran the cattle] all off the feeders and shut them away from any more feed.” Plaintiff and those who worked on his farm, assisted by many local and state officials, then began an investigation to determine the cause of the death and illness of the animals.
The local veterinarian arrived “at dark.” He found several cattle dead, several dying, and others that appeared to be normal. After treating the living animals, the veterinary performed an autopsy on one at the place where it died.
During the next week, samples of the corn, the Pro-Blend 50, the peanut vines, and the feed mixture were taken from various locations pertinent to the feeding process. Subsequent laboratory analysis and expert opinion revealed that the plaintiffs loss was caused by organic phosphate poisoning. Once the chemical agent causing the death and illness of the cattle was readily identified, the investigation focused on the source of the poison ingested by the cattle.
Chemical analysis of the samples taken from the two cattle feeders, from the main chamber of the feed mill, and from the hopper at the rear of the mill where the feed supplement was introduced, all revealed quantities of Thimet, or phorate. No Thimet was discovered in samples taken from the plaintiffs corn bins or the peanut vine barn. In addition, no poison was found in samples taken from unopened and unused bags of Pro-Blend 50 situated in the plaintiffs feed barn, or from the stock of the retailer and manufacturer at their respective business locations.
On Tuesday, January 10, a Virginia Department of Agriculture inspector, who was “a little allergic to Thimet,” detected the poison’s “pronounced” odor at both of the feeders. During the next day, when within ten feet of the feed mill, he also smelled *655Thimet. On the same day, the inspector examined a number of the empty Southern States bags that were on the floor of the feed barn and noticed the odor of Thimet in several of them.
On Monday, January 16, Herbert Jones, the County Agent for Isle of Wight, made one of his numerous trips to plaintiffs farm to assist in decontamination of the feed mill and to help in the effort to discover the source of the poison. He went to the feed storage barn and began examining the empty bags that were on the floor. While smelling inside one of the Southern States’ bags, Jones noticed a “foreign odor . . . not associated with the feed.” Upon closer examination, he saw a small residue in the “ears” at the bottom of the bag. This bag was forwarded by Jones to a State laboratory for analysis.
The chemists who examined the residue testified that phorate was found concentrated at the rate of about one and one-half pounds of the poison per 100 pounds of mixture. Also found in the residue were materials consistent with a feed supplement. In addition, a chemist determined the residue included “fragments of straw, peanut redskins, wood splinters, full rodent excretia and mass of fibers and string resembling those from burlap bags.”
The evidence showed that Doggett had used Thimet on his farm in the past as an insecticide and for rodent control. The poison had not been employed on the premises, however, after the Spring of 1976, according to plaintiff’s son, and for “four to six months prior to this [incident],” according to plaintiff.
Testimony showed Thimet was sold in 20-pound sealed bags that were packed inside a pasteboard box. After the incident in question, an empty Thimet box was found in the rear of the feed barn, a 20-by-30-foot structure. The box was about 30 feet from the bags of Pro-Blend 50 and, according to the County Agent, “had about six inches of dust on it.” The evidence showed the empty box had been in the same location for “at least” ten years. There was no “active” Thimet in the box.
The plaintiff testified there was one sealed bag of Thimet on his farm at the time of the incident. It was stored with other chemicals in a structure used as a workshop, located 50 yards from the feed barn. The evidence showed the “closed” bag of Thimet was in the same condition before and after the incident. Responding to a question by plaintiff’s counsel, plaintiff’s son denied introducing any phorate into the feed mill.
*656The retailer’s evidence showed that no chemicals or non-foodstuffs were picked up at the manufacturer’s plant along with the quantity of Pro-Blend 50 eventually sold to plaintiff, that the feed supplement was stored in the retailer’s warehouse in the sealed bags, that the supplement was sold to consumers in the original containers, and that the retailer also sold Thimet, which was kept in a location on its premises separate and apart from the Pro-Blend 50.
Southern States presented evidence describing in detail its manufacturing process which did not include the use of any phorate. It also showed that it followed “very intense” quality control procedures, that Thimet was not employed in its Richmond plant for pest control, that it never reused bags to market Pro-Blend 50, that it produces 23 different types of medicated feeds at its plant without employing Thimet, and that regular plant inspections conducted under state and federal law never disclosed the existence of phorate or Thimet on the premises.
During cross-examination, the plaintiff developed testimony to show that although the chemical Thimet was not used at the manufacturer’s plant in pest control, “organo-phosphates,” a poison that is “part of the general organic phosphate group,” was so used there. Also, plaintiff showed that many of the components of Pro-Blend 50 came to the Southern States plant from external sources, such as farms and flour mills. Among these components are, for example, soy beans, soy bean meal, wheat middlings or bran, molasses from sugar cane processors, dicalcium phosphate, vitamin supplies, and trace mineral supplies.
In addition, plaintiff showed that during the quality control at its Richmond plant, Southern States did not “run tests there for Phorate or Thimet” in the Pro-Blend 50. The manufacturer’s manager of quality control testified that because Southern States does not “use Thimet” at the plant, it did not employ the “rather complicated [testing] procedure which requires a lot of instrumentation” to test for Thimet. The same witness admitted stating in a pre-trial deposition that reused bags, if cleaned by a bag dealer, were employed on occasion by Southern States.
On appeal, defendants argue the plaintiff failed to establish a prima facie case. Under the granted instructions, to which there was no objection and which thus became the law of this case, the jury was permitted to fix liability against both defendants upon the same theory. The theory was that defendants breached their *657implied warranty of merchantability or “fitness for the ordinary or general purposes” for which Pro-Blend 50 was sold, and that such breach was the sole proximate cause of the death and injury to plaintiff’s cattle. The trial court specified that in order to recover under the warrranty theory, plaintiff must show (1) that the Pro-Blend 50 was unreasonably dangerous for the use to which it would ordinarily be put, and (2) that such condition existed when the goods left the Southern States plant. See Logan v. Montgomery Ward, 216 Va. 425, 428, 219 S.E.2d 685, 687 (1975). Accord, Featherall v. Firestone, 219 Va. 949, 963-64, 252 S.E.2d 358, 367 (1979). Because the evidence was clear that plaintiff’s loss was caused by Thimet in the feed ingested by the animals, the factual dispute was whether the poison was in the Pro-Blend 50 mixed by plaintiff’s son with the other components of the cattle feed and, if so, whether such contamination was present when the feed supplement left the manufacturer’s plant. We hold the proof was sufficient to make out a jury issue on these inquiries.
Manifestly, this is a circumstantial evidence case; and breach of warranty may be established by such evidence. Although the fact-finder is not authorized to indulge in speculation or guesswork, this does not destroy the weight of circumstantial evidence in fixing civil liability. “Proof of facts from which it can be reasonably inferred that an act or circumstance sought to be established occurred or existed is sufficient to authorize submission of the issue to the jury.” Richardson v. Lovvorn, 199 Va. 688, 692-93, 101 S.E.2d 511, 514 (1958). But such circumstantial evidence must be sufficient to establish that the result alleged is a probability rather than a mere possibility. Doane v. Farmers Cooperative Co., 250 Iowa 390, 395, 94 N.W.2d 115, 117 (1959) (seller of corn used as a cattle feed held liable for death and sickness of cattle resulting from insecticide poisoning). See Peckham v. Eastern States Farmers' Exchange, 134 F.Supp. 950 (D.R.I. 1955), aff’d per curiam, 234 F.2d 488 (1st Cir. 1956) (owner of dairy cows that died due to poisoning entitled to recover damages from seller of grain feed). See generally, Annot., “Liability of manufacturer or seller for injury caused by animal feed or medicines, crop sprays, fertilizers, insecticides, rodenticides, and similar products,” 81 A.L.R.2d 138.
In the present case, the circumstances established by the evidence are sufficient to permit a jury reasonably to infer that Thimet was in the Pro-Blend 50 fed to plaintiff’s cattle and that it *658was present in the bags when the supplement in question left the manufacturer’s plant. The evidence shows the following facts.
Plaintiffs son opened two, sealed bags of Pro-Blend 50 on the Saturday in question. The bags were part of a quantity of supplement manufactured at Southern States’ plant and packed there in the sealed containers. The bags moved in the stream of commerce in the sealed condition to the retailer and then to the consumer where they were stowed by him in that condition.
The supplement then was poured manually from the previously unopened bags into the rear hopper of the empty feed mill to be mixed with corn. Testing showed no poison existed in the corn bins. But testing also showed a quantity of Thimet in the “ears” of one of the bags, which was found in the pile of empties where the two bags used Saturday had been thrown. And a strong odor of the poison was present in a number of these bags immediately after the occurrence. In addition, chemical analysis of samples taken from the rear hopper and the main chamber of the mill revealed quantities of phorate.*
The mixture of corn and supplement remained in the mill under a shelter from Saturday afternoon to Monday morning. There was no tampering with the mill during that period.
On Monday morning peanut vines were added to the mill. Tests showed no poison in the samples taken from the vine barn. Then the cattle were fed and became ill. Samples of the substance in the feeders showed the presence of Thimet.
If the jurors, as they were entitled to do, accepted the foregoing facts, they could reasonably infer that the cattle were poisoned because Thimet was in the Pro-Blend 50 ingested by the animals, and that it was sealed within the bags used by plaintiffs son when the containers left the manufacturer’s plant.
The defendants dwell on a number of facts, some of which, if accepted by the jury, would justify a finding against the plaintiff, and others of which promote pure speculation. For example, they point to the son’s failure to notice any odor of Thimet when he emptied the bags on Saturday. Also, they point to the extraneous foreign matter found in the residue of the one bag and suggest the poison “found its way into the bag by other external causes such as nest-building by a rat.” Defendants also suggest that contami*659nation may have been due to an “accident on the farm” or because Thimet was used “carelessly around many places on the farm.” These conclusions are but examples of the inferences favorable to defendants that may have been drawn from the evidence as a whole, which evidence, as we have demonstrated, supports equally compelling inferences favorable to the plaintiff. Under these circumstances the trial court did not err in submitting the case to the jury.
Defendants have assigned two other errors which merit only passing comment. The bag in which the residue was found was received in evidence over Southern States’ objection. Even if the bag, examined by Jones a week after the incident, was not properly authenticated or identified as one of the two emptied by the son on January 7, and was thus improperly admitted, such action of the court was harmless error. Actually, introduction of the bag in evidence was unnecessary from the plaintiff’s standpoint, given the detailed testimonial evidence describing the bag, its location, the residue, and the smell of Thimet about the pile of bags, all of which testimony was received without objection.
Finally, the trial court did not err in refusing Instruction 9A, offered by Southern States, permitting the jury to find that “one of several things” caused plaintiff’s damage. The instruction was misleading under these facts because the evidence was uncontradicted that Thimet poisoning caused plaintiff’s loss. The proffered instruction was also cumulative because its substance was adequately covered by numerous instructions tendered by defendants and given.
For these reasons, the judgment of the trial court will be
Affirmed.
The evidentiary weight to be given the analysis of these samples is somewhat diminished because presumably they were taken after the Monday feeding in question and after the mill had been partly refilled.