A person does not convey [corpse-] tumah until his soul departs, even if he is fatally wounded or even if he is moribund. [Similarly,] he [still] binds [his dead brother’s wife] for yibum, releases [her] from yibum, entitles [his wife] to eat terumah, and disqualifies [her] from [eating] te-rumah. Similarly, domesticated and wild animals do not convey tumah until they have died. [If] their heads were severed, they are tamei, even if they are [still] moving convulsively; [the movements are] like the [severed] tail of a lizard that is moving convulsively.