Small creature with nothing to think about (5)
I believe the answer is:
mouse
'small creature' is the definition.
(I've seen this before)
'nothing to think about' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'to think' becomes 'muse' (to muse on something is to think about it).
'about' is an insertion indicator.
'o' going into 'muse' is 'MOUSE'.
'with' is the link.
(Other definitions for mouse that I've seen before include "Small rodent and cursor controller" , "control of computer system" , "Cursor control" , "One sitting by computer" , "PC device" .)