Two-headed teacher is beast (5)
I believe the answer is:
llama
'is beast' is the definition.
(I've seen this before)
'two-headed teacher' is the wordplay.
'two-headed' becomes 'l' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'teacher' becomes 'lama' (a lama is a spiritual teacher in Buddhism).
'l'+'lama'='LLAMA'
Can you help me to learn more?
(Other definitions for llama that I've seen before include "South American carrier" , "S American animal like a camel with soft hair" , "A native of South America" , "South American pack animal" , "one to chew the cud" .)