We finally have an answer: The beginning and the end of the sliding motion that produces static electricity experience different forces – resulting in a charge differential between the front and the back that results in the crackle of static electricity.
Like things we thought we nailed down in the 19th century and haven’t thought to revisit with modern methods and equipment. Then someone decides to look at it again and uncovered a boatload of previously unknown data.
“We thought we understood hiccups, but this changes EVERYTHING!”
(I dunno if hiccups are secretly a scientific black box or not, but you get the idea.)