2,424. What a K'zayis Includes

Maachalos Assuros 14:3

The volume of an olive discussed in the previous halachos doesn’t include what’s between one’s teeth but it does include what’s between one’s gums; This is because his mouth benefited from an olive’s volume of food. Even if one ate half an olive’s volume, spit it up and re-ate the same piece, he’s liable because liability is based on the benefit one’s mouth receives from the prohibited item.

Maachalos Assuros 14:4

If an olive’s volume of forbidden fats, neveila (an animal that died), piggul (sacrifices offered with improper intention), nosar (sacrifices left over past their times), etc. was left in the sun and it shriveled in size, one is not liable for eating it. If it was later left in the rain and it expanded, one is again liable for kareis or lashes. If it was originally smaller than an olive’s volume and it expanded to the size of an olive, it is prohibited to eat but one isn’t liable to lashes for doing so.