The term 'MOUSE SOUND' can be broken down into three crossword solutions: CLICK (5 letters), GNAWING (7 letters), and SQUEAK (6 letters). These words refer to the sounds that mice make. A mouse's CLICK is a sharp, short sound made when it moves its feet. Gnawing is the sound of a mouse chewing on something, usually wood or plastic. Finally, a mouse's SQUEAK is a high-pitched sound made when it is startled or scared.