Hullin 24: Staying Youthful by Standing on One Foot

2 tiny mishnayot: 1 - There is that which is problematic for kohanim - to do the Temple service (namely blemishes) - that are not a problem for levi'im (Levites), and vice versa, where Levites can only serve at certain ages of majority and not for life. 2 - There is that which is impure for earthenware vessels that is pure for all other vessels, and vice versa. The Gemara goes on to explain the details of these cases.