Mules regain energy rapidly when allowed to rest.

Evidence

Any mule, no matter how old he is, that is not worked for a couple of weeks gets as frisky as a colt, his ears are always up, and he farts a lot. — Crews, Harry, A childhood the biography of a place, 914

Categorization

• corroborated: 2 independent passages support this claim — Crews, Harry, A childhood the biography of a place, 914