Creature a vet rushes to treat - second stops ... (7,5)
I believe the answer is:
harvest mouse
'creature' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'a vet rushes to treat second stops' is the wordplay.
'a vet rushes' becomes 'harvest' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to treat' becomes 'use' (using is a kind of treating).
'second' becomes 'mo' (both are short periods of time).
'stops' is an insertion indicator (to stop can mean to block a gap).
'harvest'+'use'='harvestuse'
'harvestuse' placed around 'mo' is 'HARVEST MOUSE'.
(Other definitions for harvest mouse that I've seen before include "Smallest British rodent" , "rural resident" , "Cornfield rodent" .)