Monsters mostly guzzle on bison’s heart (7)
I believe the answer is:
gorgons
'monsters' is the definition.
(I know this)
'mostly guzzle on bison's heart' is the wordplay.
I cannot really understand how this works, but
'on' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for gorgons that I've seen before include "Mythical Greek sisters whose look turned people to stone" , "Three winged sister monsters with 'hair' of writhing snakes" , "fierce women" , "Ugly sisters" , "Monstrous sisters" .)