We're using bodies evolved for hunting, gathering, and gratuitous violence for information age tasks like word processing and spreadsheet tweaking.
Gesture: any physical movement that can be sensed and responded to by a digital system without the aid of a traditional input device such as a mouse or stylus.
Avoid putting essential features or information like a label below an interface element that can be touched, as it may become hidden by the user’s own hand.
The complexity of the gesture should match the complexity of the task at hand.
The best designs are those that “dissolve into behavior.”
The best, most natural designs, then, are those that match the behavior of the system to the gesture humans might already do to enable that behavior.