mouse droppings

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.