I know how your lot's minds work These balls:

Both mine LOOOOOOOOVE the one on the bottom right, the 'strappy' one I call it. They're also OK with the top left one, the 'sticky' one. But they're not much keen on the middle one, the 'cordy' one. Any idea what they're made of, and if I can bulk-buy them individually (i.e. just one type) from somewhere?