I love it when cats do cat things, like assume a hunter's pouncing position or take great leaps. I also love it when boys do little boy things.
And so I smile whenever Theo pushes around a toy truck, car, bus, or train. He says "choo choo" when pushing the train and "vroom" when pushing the car. Sometimes he'll push the bus and say "choo choo," but I think he just likes to get a rise of us, since we say "noooooooooooooooo, Vroooooooom." It makes him laugh.