one time, I had a female give birth to a bunch of still borns, and 5 of them had bitten themselves in the side before they died. It was an odd thing to see... I have also had the occasional young snake bite itself upon death. One of my theories as to why they may do that is possibly the snake feels pain and in all of it's confusion, is actually trying to bite the "attacker" that is causing the pain. It's just a though... we will probably never know why they do this!