fine-tooth comb

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A comb with teeth set close together.
• noun A method of searching or investigating in minute detail.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A comb with fine, closely-spaced teeth.
• verb To go over or through with a fine-tooth comb
• verb To search meticulously.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a comb with teeth set close together
• noun a method of examining in minute detail