That hurt pet slipping lead (4)
I believe the answer is:
ouch
'that hurt' is the definition.
(expression of pain)
'pet slipping lead' is the wordplay.
'pet' becomes 'touch' (to pet an animal is to touch it affectionately).
'slipping lead' means to remove the first letter (I've seen 'slips lead' mean this).
'touch' with its first letter taken off is 'OUCH'.
(Other definitions for ouch that I've seen before include "that hurts!" , "Exclamation of pain - that hurt!" , "Pained cry" , "Pained sound" , "Ruby, perhaps once in it" .)