1
general::
Phrase(s): smell a rat
to suspect that something is wrong; to sense that someone has caused something wrong. • I don’t think this was an accident. I smell a rat. Bob had something to do with this. • The minute I came in, I smelled a rat. Sure enough, I had been robbed.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Suspect something is wrong, especially a betrayal of some kind. For example, When I didn't hear any more from my prospective employer, I began to smell a rat. This expression alludes to a cat sniffing out a rat. [c. 1550]
American Heritage Idioms