Active vet got hen to accompany duck (2,3,2)
I believe the answer is:
on the go
'active' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for on the go that I've seen before include "Running around busily" , "Ever busy" , "Moving -- active" , "Very active (colloq.)" , "Active, always doing something" .)