....

A zipper edge on a skinning knife is pretty handy, but a skilled hunter can readily use the tip of his hunting blade and the index and middle fingers of his off hand to do the same task. Once a slit is made in the hide, it is pretty easy to slip the two fingers underneath and ride the tip in between the fingers and at an angle so the blade edge will sever the hide as it is drug along a line with the fingers guiding it along. Done properly, the risk of overpenetration is insignificant.

....