The correct answer is C. To suspect foul dealings.
The phrase “to smell a rat” means to suspect that something is wrong or dishonest. It is often used in business or politics, when someone suspects that someone else is trying to deceive them. The phrase is thought to have originated in the 16th century, when rats were often associated with disease and death. If someone saw a rat in a place where it was not supposed to be, it would be a sign that something was wrong.
The other options are incorrect. Option A is incorrect because the plague is not caused by rats. Option B is incorrect because the smell of a dead rat is not necessarily a sign of foul dealings. Option D is incorrect because being in a bad mood is not the same as suspecting foul dealings. Option E is incorrect because the phrase “to smell a rat” is not a literal phrase.