Just read about "rabbit functions", a term for math expressions that are essentially "pulled out of a hat"! Love it, and have to use this in a paper some day.
From "Wachspress 1975, A Rational Finite Element Basis:
"A "rabbit function" is a function that is pulled out of a hat. When a magician pulls a rabbit out of a hat, the effect astonishes the onlookers. Once the illusion is revealed, the rabbit generation is
no more surprising than the generation of rabbits by rabbits."