Chullin 124 - Pieces of Meat on a Hide
If a hide has an olive's volume of dead meat ( nevelah ) attached to it, that piece of meat is ritually impure. If one touches it through a sliver attached to it, the sliver acts as a handle and transmits impurity to the person. A hair on the other side of the hide is regarded as a protector to the meat and transmits impurity from it, since it goes through the hide.
If there were two half-olive volumes of meat attached to the hide, they add up when they are carried, and thus transmit impurity to the one who carries the hide. However, if one touches them, even at the same time, he does not become impure, because these are two separate acts of contact - these are the words of Rabbi Ishmael. Rabbi Akiva says that the two half-olive volumes of meat are nullified by the hide and do not transmit impurity at all. That is because through his actions of separating meat from the hide, the butcher showed that he does not consider the pieces significant. Even Rabbi Akiva agrees that if one stuck the two pieces of meat on a splinter and moved them, he becomes impure.
Art: Bartolomeo Passerotti - The Butcher's Shop