Billy laughed. "I don't touch food experiments. I've learned that it never ends well for me. But that...that's amazing. You save people without us knowing that we're ever in trouble?"

Why? He liked humanity and liked to help out, apparently, but it seemed there had to be more to it. Billy's reasons were similar, but he'd had the toys to play with as incentive too. The TARDIS had to be better than any toy, of course...

"I guess you never stick around long enough for the newspapers to notice you."