We hear girl studied a South American snake (8)
I believe the answer is:
anaconda
'south american snake' is the definition.
(anacondas are native to South America)
'we hear girl studied a' is the wordplay.
I cannot really see how this works, but
'girl' could be 'con' and 'con' is found within the answer.
'a' could be 'an' and 'an' is present in the answer.
The remaining letters 'ada' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for anaconda that I've seen before include "Large semiaquatic snake" , "S. Am. constrictor snake" , "South American python" , "Aquatic snake" , "Large South American snake" .)