Graduates have medium to small reptiles (6)

I believe the answer is:

mambas

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'reptiles' is the definition.
(mamba is a kind of reptile)

'graduates have medium to small' is the wordplay.
'graduates' becomes 'MA MA' (more than one holder of a Master of Arts degree).
'have' indicates putting letters inside.
'medium' becomes 'b' (I can't justify this - if you can you should believe this answer much more).
'to small' becomes 's' (abbreviation - e.g. clothes size).
'mama' placed around 'b' is 'mamba'.
'mamba'+'s'='MAMBAS'

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(Other definitions for mambas that I've seen before include "these snakes bite dangerously" , "Arboreal snakes" .)

I've seen this clue in The Mirror.

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