The last three Carls have all been able to do math. This skill is a great hit, as you can imagine, with the school children we visit. I don't really know how they do it. As far as I know, I am not giving any signal. Maybe it's some kind of mental telepathy; we are very connected. He can do the simple ones with other people, but for the harder ones, he needs me to think of the answer. If I make a mistake, he does, too.