Is it possible out-of-head Gary will get grass? (6)
I believe the answer is:
canary
'grass?' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for canary that I've seen before include "Bird from an island group" , "Songbird once used to detect toxic gases in mines" , "Kind of yellow" , "Bright yellow finch" , "Caged song bird" .)