A: Jake smelled a rat in his company when some of his private documents about a new product went missing.

    B: What did he do then?

    A: He reported to the police and it turns out that one of his employees sold them to a competitor.

    Note: This idiom describes a feeling that something is not quite right, but the person is unable to discern exactly what it might be. The theory behind this idiom might involve a cat being able to smell a rat nearby, despite not having caught sight of it. After picking up a rat’s scent, a cat perceives that something is not quite right, but without having seen the rat, the cat is unable to confirm its feelings. The phrase has been in use in the press since the 1900s.