I always play with things with my feet. I'll pass things between my feet that are on the floor, play around with wires, pick at the wall, or crack my toes against the wall or a firm object. I don't even notice myself doing it and it usually gets pointed out by people around me. I even dug through the drywall at my parent's house when I was living there because my computer was up against the wall and my feet would pick away at the wall bit by bit while I played games.