Sound of this snake! (4)
I believe the answer is:
hiss
'sound' is the definition.
(hiss is a kind of sound)
'of this snake' is the wordplay.
'of' says the answer is hidden in the clue.
'HISS' is hidden within 'this snake'.
(Other definitions for hiss that I've seen before include "Urgently whisper" , "Make sibilant sound like snake" , "less welcome sign?" , "S-s-snake's s-s-sound?" , "Sound of escaping gas" .)