Last two say hens, bizarrely, sound like they're laughing (6)
I believe the answer is:
hyenas
'hens bizarrely sound like they're laughing' is the definition.
The definition suggests an adverb but the answer is not.
'last two say' is the wordplay.
'last two' becomes 'hyen' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'say' becomes 'as' (I've seen this in other clues).
'hyen'+'as'='HYENAS'
Can you help me to learn more?
(Other definitions for hyenas that I've seen before include "Dog-like animal of Africa" , "Nocturnal carnivouous mammals of Asia and Africa" , "Dog-like nocturnal carrion feeders" , "Dog-like animals that sound as if they laugh" , "Dog-like animals with cry like human laughter" .)