There are three who must shave their hair and their shaving is a Torah obligation: a nazir (nazirite), a metzora (“leper,” but not really) and the Leviim (Levites). If any of these shave with something other than a razor, or if they leave even two hairs remaining, then they have done nothing at all.
The two birds used in the purification of the metzora must be alike in appearance, size and price, and they must be purchased at the same time. If they are not alike, they are valid after the fact; the same is true if one was purchased on one day and the other on the next. If after one of the birds was slaughtered it was found not to be a free bird, a partner is bought for the second and the first may be eaten. If after the bird was slaughtered it was found to a treifa, a partner is bought for the second and one may derive benefit from the first. If the blood of the slaughtered bird got spilled, the bird that was to be released must be left to die (and two new birds brought). If the bird that was to be released died, the blood of the slaughtered bird must be spilled out (and two new birds brought).