When I was a boy my dog got hold of a possum and left it for dead, or so we thought. It was bleeding and barely breathing.
Being the kind soul that I was at 14, I decided it needed putting out of its misery, so I shot it.
Much to my surprise, it suddenly burst to life and began running around and hissing. Realizing that I was the cause of this poor creature's new found suffering, I did what any self respecting person would have done, I shot again.

Possums really do play possum