From the given options choose the word that most clearly explains the idiom-

"To smell a Rat"

To suspect a trick or deceit

The idiom "to smell a rat" most clearly explains to suspect a trick or deceit. The idiom comes from the literal meaning of detecting the presence of a rat, which is a small, furry animal that is often associated with deception and trickery. In the same way, when someone "smells a rat," they are suspicious that something is not right or that someone is trying to deceive them.

The other options are not as accurate. To smell a foul smell means that someone can detect a bad odor. To see a dead rat means that someone has seen a rat that has died. To misunderstand means that someone has misinterpreted something that has been said or done.