Chulin 9:3-4

Chulin 9:3

(The Mishna now addresses how much skin must be removed from the flesh to no longer count as attached vis-à-vis ritual impurity.) If one flays a domesticated or a wild animal, either kosher or non-kosher, whether small or large, in order to make a rug, the measure is enough to grab hold of (i.e., two handbreadths – about six inches). If he flayed the animal to make a water skin, the skin is considered attached until the animal's chest has been flayed. If he starts skinning the animal from its feet, then everything is a considered connected to the flesh in order to receive or to transmit ritual impurity. Rabbi Yochanan ben Nuri says that the skin of the neck is not considered connected but the Sages say that it is considered connected until he flays all the skin.

Chulin 9:4

If there is an olive-sized piece of flesh on an animal’s hide and a person touches a shred extending from it or a hair on the opposite side of the hide from it, he is rendered ritually impure. Rabbi Yishmael says that if there are two half-olive-sized pieces on a hide, they convey ritual impurity through carrying the hide but not through contact; Rabbi Akiva says that it doesn’t convey ritual impurity – not through contact and not through carrying. Rabbi Akiva does agree that if there were two such pieces of flesh of half an olive’s volume each and he put them on a chip of wood and moved them, then he is rendered ritually unclean. The reason that Rabbi Akiva declares one ritually clean in the case of the hide is because the hide negates the flesh.