Checks closely (4)
I believe the answer is:
vets
'checks closely' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for vets that I've seen before include "Siegfried and Tristan Farnon, for example" , "Screens the animal doctors" , "Ex-servicemen and women, in short" , "Screens for the job perhaps" , "Investigates thoroughly to ensure suitability, for a job perhaps" .)