(n) A botfly larva. The parent fly lays its eggs in a person or animal, and the larva grows into a huge maggot that migrates to the neck and chews its way out when it is ready to pupate. Also spelled warble, wormil.
The rabbit was dead, but we could see that its neck was moving as if it had an alien under its skin, and the next thing we knew, a giant worble the size of a shotgun shell crawled out of it. And we figured that rabbit was better off dead.