Fracture one's fingers? (4)
I believe the answer is:
snap
'fracture' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for snap that I've seen before include "Break under strain" , "Break off - card-game" , "Unpremeditated - bite" , "Become unhinged" , "that's a copy!" .)