(concurring). While concurring with the majority opinion, I believe further comment is in order concerning burden of proof. The instructions on burden of proof were in error because special circumstances did exist in this case, sufficient to shift to the defendants the burden of showing which of them manufactured the broken *173lens. Snider v Bob Thibodeau Ford, Inc, 42 Mich App 708; 202 NW2d 727 (1972). Here the jury may have rested its verdict on the trial court’s instruction that, in the absence of evidence indicating which of the two defendants was liable, the jury should return a verdict in favor of both defendants. Or the jury may have concluded that regardless of any violation of Federal record-keeping requirements under 21 CFR § 801.410, the lens in question was not defectively made. Where the jury verdict is ambiguous and could have been based upon an incorrect jury instruction, or a finding of no negligence, a new trial is warranted. Alston v Tye, 67 Mich App 138; 240 NW2d 472 (1976).