from online descriptions of laser mouse operating principle it's unclear to me that the mouse would need to be particularly big. Is the size of the mouse really based on ergonomics considerations and it could in practice be fit into much smaller case if we wanted to? Is the mouse actually mostly empty inside? Or is the current size important for making it from cheaper components than what would have been needed for a smaller design? Also, so suppose we wanted to take an existing laser mouse and change its shape, such as in the best case to turn it into a pen shaped device like "Genius pen mouse" (TM). How hard would that be? Are the light source and sensor of the mouse straightforwardly extractable for installation in another device? How big are they? Are there any other components in the mouse that are "too big" and so would probably need to be placed outside the "pen mouse", such as in a "receiver" connected to the pen by a cable?