Definition & Meaning of "smell a rat"

What is the origin of the idiom "smell a rat" and when to use it?

The idiom "smell a rat" has its origins in the behavior of rodents, particularly the characteristic strong odor associated with rats. In the late 16th century, the phrase "smell a rat" emerged in English, initially as "to smell a rat about," referring to the suspicion or sense of something being wrong or deceitful. The phrase likely draws on the natural aversion humans have to the smell of rats, which can indicate the presence of filth or danger. Over time, "smell a rat" evolved into a metaphorical expression, signifying the detection of dishonesty, deceit, or a hidden agenda in various situations.