Smellvin
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Bort
That, and you also want to make sure it's really dead before you put it in your mouth. The last thing you need is a mouse deciding to bite you on the tongue as you're sitting down to dinner.

There seems to be endless dispute about purring too -- why do cats purr both when they're happy and when they're frightened? -- and I'll pull a possible answer out of my ass. Purring is probably useful as a way for kittens to announce their position to their mother, without tipping off predators; it's just not the sort of sound that attracts attention unless you're specifically listening for it. So when kittens are frightened, they know to purr. Purring is probably also useful when kittens are nursing or hungry so the mother knows what's going on. And because cats' brains are tiny, they will still purr even into adulthood, long after the habit has ceased to be useful.