I was going to say most animal births ive seen the mommas bite it. Ive never seen them just leave it, but maybe some animals do. I have actually done a lot of research on this before giving birth. Leaving the umbilical cord attached for too pong actually causes jaundice (my youngest was on belli lights for two weeks afterwards). The best way to tell when to cut the cord is when it stops pulsating. Either way though- instant cutting of the cord is not the healthiest option.