*Artist's inspiration (5)
(Other definitions for mouse that I've seen before include "PC device" , "Domestic rodent" , "underhand office worker?" , "Cursor control" , "computer equipment" .)
'artist's inspiration' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for muse that I've seen before include "Inspiring goddess" , "Goddess; rock group" , "Ponder, say meditatively" , "Think - goddess of the liberal arts" , "Source of inspiration; rock group" .)