(Devarim 25:4) "You shall not muzzle an ox in its threshing": This tells me only of an ox. Whence do I derive (the same for) an animal and a bird? From "in its threshing" (i.e., the threshing is the critical factor). If so, why is it written "ox"? You may not muzzle an ox, but you may "muzzle" a man (i.e., if you keep him from eating while working, you do not receive stripes, as you do for muzzling an ox.)