How do cows vocalise depression? (3)
I believe the answer is:
low
I believe this clue is a double definition.
'how do cows vocalise' is the first definition.
(low can mean to make a mooing sound)
'depression?' is the second definition.
(I know that depression can be written as low)
(Other definitions for low that I've seen before include "something from Guernsey?" , "Not high or tall" , "Dejected; moo" , "Inferior; moo" , "Deep sound made by cattle" .)