I dunno, I suppose that legally it could be owned by somebody who could then come and claim it. But morally, to me, an owner who keeps their cat primarily outside, and doesn't put a collar or microchip on the cat, really doesn't care about the cat. So if I didn't have any cats, and felt bad for this one, and liked it, I would probably take it to the vet to check for a microchip and check it's health (get shots etc), then try it out as an indoor(only) pet, with the understanding that it's original "owner" could come and claim him at any time (or post "missing" posters or whatever), at which point I'd give him up.

That's probably what I would do.

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The little monsters 3