Whatever a mouse user is doing, he is perpetually hovering. He might be hovering over a specific control, or over several places in the course of another action: dragging a scrollbar, selecting a word, even just idling around the screen. But until he has clicked, this user has taken no positive action. A click is unambiguous: the caveman pointing at the mammoth, the dog scratching at the door to go out. It cannot be done in the course of anything else.