Parasites giving signs of approval (5)
I believe the answer is:
ticks
I believe this 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' is the 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" .)