"Things," he says, with great authority, and then grins. "Actually not very many things. I tried to build a robot puppy once but I did not succeed. That's what trying again is for, though! The latest thing I'm working on is stairs. Because we have a Roomba, and they're really only good for relatively unobstructed flat surfaces, and stairs get dirty too, so I'm trying to build a robot that can climb up and down stairs, and then I'll figure out how to make it also vacuum them."