What toffee may be said to do during mastication (5)
I believe the answer is:
stick
This might be a double definition.
'what toffee may be said to do during' is the first definition.
The definition suggests a singular noun which matches the answer.
'mastication' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
Can you help me to learn more?
(Other definitions for stick that I've seen before include "Adhere - cane" , "Endure" , "heavy criticism" , "Tolerate" , "School punishment once" .)