A natural food crusher (3)
I believe the answer is:
boa
'crusher' is the definition.
(I've seen this in another clue)
'a natural food' is the wordplay.
'a natural' becomes 'bo' (I can't explain this - if you can you should believe this answer much more).
'food' becomes 'A' (A is an example).
'bo'+'a'='BOA'
Can you help me to learn more?
(Other definitions for boa that I've seen before include "S American snake that crushes its prey" , "Wrap" , "... cold-blooded creature" , "Non-venomous snake" , "Fluffy scarf of feathers" .)