mouse droppings n.
[MS-DOS] Pixels (usually single) that are not properly
restored when the mouse pointer moves away from a particular
location on the screen, producing the appearance that the mouse
pointer has left droppings behind. The major causes for this
problem are programs that write to the screen memory
corresponding to the mouse pointer's current location without
hiding the mouse pointer first, and mouse drivers that do not
quite support the graphics mode in use.