Mock, jeer (4)
I believe the answer is:
hiss
I believe this clue is a double definition.
'mock' is the first definition.
(thesaurus)
'jeer' is the second definition.
(I've seen this before)
(Other definitions for hiss that I've seen before include "Catcall" , "Make disapproving sound" , "Sound of serpent" , "Sharp sibilant sound" , "Sibilant sound made through the teeth" .)