Sift through (4)
(Other definitions for comb that I've seen before include "Fowl's crest" , "Search well; bird's crest" , "Carefully search" , "Honey structure" , "Toothed grooming implement" .)
'sift through' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cull that I've seen before include "Selectively slaughter" , "Kill surplus animals in herd" , "Remove from herd" , "Pick (best); kill off (weakest)" , "Select and destroy inferior specimens" .)