Idiom meaning, usage examples, facts

1. That professor goes over his students’ research papers with a fine-tooth comb looking for mistakes. If there are any, he finds them.
2. The police examined the crime scene. They went over it with a fine-tooth comb, but they couldn’t find any.

The expression suggests the idea that if something can be found (i. e. , if it exists), it can be found by using a comb with very fine (i. e. , closely spaced) teeth.