fine-tooth comb, to go over with a

go over (something) with a fine-tooth comb

To scrutinize something; to look at something very carefully. We need to go over these files with a fine-tooth comb to find that missing paperwork. Make sure to go over your thesis with a fine-tooth comb before you hand it in—you don't want your advisors wading through proofreading errors, do you?

go over something with a fine-tooth comb

and search something with a fine-tooth comb; go through something with a fine-tooth comb

Fig. to search through something very carefully. I can't find my calculus book. I went over the whole place with a fine-tooth comb. I searched this place with a fine-tooth comb and didn't find my ring.

fine-tooth comb, to go over with a

To search for or investigate with scrupulous care. Although combs have been known since the time of ancient Egypt, and presumably some had finer teeth than others, the term “fine-tooth comb” dates only from the first half of the nineteenth century. The transfer of combing out nits to other kinds of search or investigation took place only in the late nineteenth century.