Joking aside, this is Marvin Minsky's paper "Jokes and their Relation to the Cognitive Unconscious", published in Cognitive Constraints on Communication, Vaina and Hintikka (eds.) Reidel, 1981. More fun than a barrel of an infinite number of monkeys.
https://web.media.mit.edu/~minsky/papers/jokes.cognitive.txt
>Abstract: Freud's theory of jokes explains how they overcome the mental "censors" that make it hard for us to think "forbidden" thoughts. But his theory did not work so well for humorous nonsense as for other comical subjects. In this essay I argue that the different forms of humor can be seen as much more similar, once we recognize the importance of knowledge about knowledge and, particularly, aspects of thinking concerned with recognizing and suppressing bugs -- ineffective or destructive thought processes. When seen in this light, much humor that at first seems pointless, or mysterious, becomes more understandable.
>A gentleman entered a pastry-cook's shop and ordered a cake; but he soon brought it back and asked for a glass of liqueur instead. He drank it and began to leave without having paid. The proprietor detained him. "You've not paid for the liqueur." "But I gave you the cake in exchange for it." "You didn't pay for that either." "But I hadn't eaten it". --- from Freud (1905).
>"Yields truth when appended to its own quotation" yields truth when appended to its own quotation. --W. V. Quine
>A man at the dinner table dipped his hands in the mayonnaise and then ran them through his hair. When his neighbor looked astonished, the man apologized: "I'm so sorry. I thought it was spinach."
>[Note 11] Spinach. A reader mentioned that she heard this joke about brocolli, not mayonnaise. This is funnier, because it transfers a plausible mistake into an implausible context. In Freud's version the mistake is already too silly: one could mistake spinach for broccoli, but not for mayonnaise. I suspect that Freud transposed the wrong absurdity when he determined to tell it himself later on. Indeed, he (p.139) seems particularly annoyed at this joke -- and well he might be if, indeed, he himself damaged it by spoiling the elegance of the frame-shift. I would not mention this were it not for the established tradition of advancing psychiatry by analyzing Freud's own writings.
>ACKNOWLEDGMENTS: I thank Howard Cannon, Danny Hillis, William Kornfeld, David Levitt, Gloria Rudisch, and Richard Stallman for suggestions. Gosrdon Oro provided the dog-joke.