Is a box cutter an inherently dangerous weapon?

We conclude that the trial court's instruction defining a "dangerous weapon" to include an "inherently dangerous" object entails the presentation of a legally (rather than factually ) invalid theory. There was no failure of proofthat is, a failure to show through evidence that the box cutter is an "inherently dangerous" weapon. Instead, a box cutter cannot be an inherently deadly weapon "as a matter of law." ( McCoy , supra , 25 Cal.2d at p. 188, 153 P.2d 315.) This is functionally indistinguishable from the situation in which a jury is instructed that a particular felony can be a predicate for felony murder when, as a matter of law, it cannot be. Because this latter situation involves the presentation of a legally invalid theory ( People v. Smith (1984) 35 Cal.3d 798, 808, 201 Cal.Rptr. 311, 678 P.2d 886 ), so does this case.

Further, we must vacate the assault conviction because there is no basis in the record for concluding that the jury relied on the alternative definition of "deadly weapon" (that is, the definition looking to how a non-inherently dangerous weapon was actually used). ( People v. Smith (1998) 62 Cal.App.4th 1233, 1239, 72 Cal.Rptr.2d 918 [reversal required where appellate court "cannot discern from the record which theory provided the basis for the jury's determination of guilt"].) Indeed, the prosecutor in his rebuttal argument affirmatively urged the jury to rely on the legally invalid theory when he called the box cutter an "inherently deadly weapon." And because the trial court used the same definition of "deadly weapon" for both the assault charge and the personal use enhancement, both suffer from the same defect, and both must be vacated.