"We had cats, when I was a kid," he says. "I know some people have them aboard here. I've seen some sneak out into the hallways and then get confused."

It's happened to him twice. Pick the cat up, read its tag, ask the computer where it belongs, take it back to its owners' room. Sneaky little things, but he loves them.

"We don't have leftovers. The replicators just turn whatever's left back into energy. That way we don't have to store any food."