Words used as figures of speech usually don't mean the same thing as the literal use of the words themselves. They are quaint sayings, little snippets of the English language, that are used as descriptions of something or some condition. A figure of speech I have used recently in my class room in describing the physical attraction between oppositely charged magnetic poles is "they go together like peas and carrots". That is a familiar quotation from the movie "Forrest Gump". Speaking of Forrest Gump, Tom Hank's famous character had a nice figure of speech: "Life is like a box of chocolates; you never know what you're going to get."
Figures of speech are used to describe the way things go together, like "two peas in a pod". They can also be used to describe loyalty towards another person, such as "I got your slack". They can be used to describe just about anything, such as a great pitch in baseball: "That's putting some pepper on the 'ol fastball". They can also describe degrees of sickness, or physical ailment: "I was as sick as a dog".