It’s hard to explain puns to kleptomaniacs because….
…they’re always taking things literally!
Why is it funny?
“Literal” means relating to the exact meaning of words, rather than to their implied meaning in context.
How someone “takes something” is how they interpret, understand, or react to it.
“Taking things literally” is a fixed phrase that refers to not being able to understand abstractions or metaphors.
If you said, “That exam was a piece of cake,” to someone who only took things literally, they might say, “It wasn’t cake, it was an exam.” You can imagine that someone like that wouldn’t get many jokes!
“Taking things,” as a phrase on its own, can mean “stealing things.” A “kleptomaniac” is a person who compulsively steals things, so they’re “always taking things,” and the “literally” after the phrase means that the phrase coming before it should be understood *exactly* as it was written, with no other meaning.
Now the joke made you “take things literally” by reading the words “take things” literally!