Make a note about him starting to squirm (6)
I believe the answer is:
writhe
'squirm' is the definition.
(synonyms)
'make a note about him starting' is the wordplay.
'make a note' becomes 'write' (write a note down).
'about' means one lot of letters goes inside another.
'starting' suggests taking the first letters.
The first letter of 'him' is 'h'.
'write' placed around 'h' is 'WRITHE'.
'to' is the link.
(Other definitions for writhe that I've seen before include "Squirm in pain" , "'Twist, squirm (6)'" , "Move sinuously" , "Painfully move" , "6, maybe in agony" .)