I wasn't originally going to get a brain transplant

This joke is a classic example of wordplay, specifically a pun that hinges on the phrase "changed my mind." On the surface, "changed my mind" means to alter one's decision or opinion, which is a common human experience. However, in the context of a brain transplant, the phrase takes on a literal and darkly humorous meaning: the speaker literally changed their brain, and therefore their mind, for a new one.

The humor comes from this clever twist, playing with our expectations. Brain transplants are, of course, a staple of science fiction and speculative stories, often explored for their ethical and identity-related implications. The very idea of swapping out one's brain is outlandish and unsettling, making the casual delivery of the punchline even funnier as it grounds this fantastical concept in a mundane idiom.

It's this unexpected double meaning, combined with the absurd image of physically replacing one's brain, that makes the joke so effective. It's a quick, smart play on words that leaves you with a little chuckle as you untangle the literal and figurative interpretations.