Other mistake: When Wallace is eating the celery, you can see that the bottom of his throat looks really weird, as if the model wasn't complete.
Other mistake: When the rabbits are being sucked up at the start, there is light in the tunnel. This is not possible since the tunnel is underground and the pipe has got bends in it. No light should get through.
Other mistake: When Gromit is dancing and making the puppet dance, the arms of the puppet bend but they shouldn't since there is no wire connecting them.
Answer: The fall killed him, and the brain waves are seen leaving his body as he physically transforms back. Then, he's raised from the dead by the smell of cheese. (Yeah, I know, but it's a kid's movie, not a documentary.)
johnrosa