Bava Metzia 90: Muzzle It!
Trampling grain to remove the outer skin, and other threshing... Plus, the issue of muzzling animals, and how that's complicated by issues of terumah, ma'aser, ma'aser sheni, etc. And where prohibitions kick in. Also, muzzling a non-Jew's animal or having a non-Jew muzzle a Jew's animal (or castrate) - is the non-Jew included in the negative commandment or not?