Agrees with the head (4)
I believe the answer is:
nods
'agrees' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nods that I've seen before include "Non-verbal indications of assent" , "Signals assent" , "Shows assent" , "Makes mistake" , "Is careless" .)