Parasites giving signs of approval (5)
I believe the answer is:
ticks
This clue is a double definition.
'parasites' is the first definition.
(I've seen this before)
'signs of approval' is the second definition.
(I've seen this before)
'giving' acts as a link.
(Other definitions for ticks that I've seen before include "Makes noise like old clock" , "Parasitic insects" , "Parasites" , "They suck from warm-blooded animals" , "Parasitic arachnids" .)