Unit-vector-eyes-follow-mouse

A unit vector or normal vector is useful for pointing things at other things. Like pointing eyes at a mouse. See here what a unit vector is: https://en.wikipedia.org/wiki/Unit_vector

and then check out http://maciejkus.com/unit-vector-eyes/ to see some html5/canvas eyes which follow your mouse cursor. They currently only follow the mouse when it is inside the canvas element, but this can easily be changed.