When a person touches anything unclean, be it human uncleanness or an unclean animal or any unclean creature, and eats flesh from the LORD’s sacrifices of well-being, that person shall be cut off from his kin.
There are a number of opinions on what the Karet punishment is:
According to Rashi, it means that the offender’s young children may die and/or that the offender may die young .
According to Tosfot, children are only subject to death where the Torah explicitly states it.
According to the Talmud Yerushalmi, the offender dies before he turns 50.
Finally, according to the Talmud Bavli, the offender dies between the ages of 50 and 60.