Smell a Rat (Origin)

What Is the Origin of the Saying "Smell a Rat"?

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The term "smell a rat" means to suspect something is wrong or to suspect someone of betraying the group (i.e., of being an informer).

Examples of Use:

Why have they only sent the deputy leader to the meeting? I smell a rat.
I smell a rat. The offer is too good to be true.
Her husband has been working late a lot recently. She is starting to smell a rat.
How did the protestors know about the product launch? The CEO smells a rat.

This idiom is very old. It originates from at least the 16th century as evidenced by its appearance in English poet John Skelton's 1540 poem "The Image of Ipocrysy":

"But then beware the catte; For yf they smell a ratt, They grisely chide and chatt."

The saying "to smell a rat" comes from the idea of a cat hunting a rat. Just as a cat can smell that there is a rat nearby, so we can sense that something isn't quite right. The word "rat" is a metaphor for a something bad, which is hardly surprising given the plagues and diseases associated with rats.

Of note, a person in a group who secretly gives information to the authorities or an enemy is known as a "rat." Sometimes, "smell a rat" refers specifically to suspecting there is an informer in the group.

Competing Theory

Rats stink – dead rats even more so. This saying originates from the idea that we can tell a rat is present from its smell. Imagine someone moving furniture and looking in cupboards to find the source of the foul smell, a dead rat.