Cats, actually.

[ How does he explain this? Snake goes quiet for a few seconds, but whatever, he may as well just offer the truth. ]

Back on the ship we were traveling on, there was a gardens area. [ Inside the ship, yes. It had been a pretty peaceful place, all things considered. ] There was a tree in there that... sprouted kittens. Tiny ones. You ended up adopting a few.

[ There's a wave of guilt when Snake realizes he has no idea what happened to them, after Wash left and the Moira went down. ]