She's right. When the headcrab's kicked off the corpse collapses. The skull's been ruthlessly, bloodily stripped of virtually all its flesh, and the top of the cranial vault's missing. We don't suggest checking inside, either.

One particular zombie stops some distance away from the two humans, apparently trapped behind a junked fifty-five gallon drum. It lets out a horrific bellow and swings its arms crudely at the thing. The drum goes flying towards the two humans at considerable speed.