Finally my time to shine. Looking wayyy back at the history of their evolution, they come from a dinosaur (the ironically named Steadfastasaurus) which has the first ever example of a "pull switch" joint, which allowed them to fake an attack on prey. You might wonder why you would need to fake out an attack, but the answer is as simple as why boxers fake hits today; that is, their prey was a competing predator. They were known to feast on Pregdonalons which had a slow reaction speed evidenced by their diminished prefrontal cortex and amygdala, so the Steadfastasaurus would lurch forward, provoking the Pregdonalon, before immediately counter striking and having a succulent Chinese meal.

It should be noted that I made all this up and have no idea what I'm talking about

From what I very vaguely remember, the idea is that they're (somewhat accidentally, just by instinct) causing a reverberation in the ground that seems, to worms, like rain. Making the worms (somewhat accidentally, just by instinct) go "aww shit, this lovely dirt hangout spot is boutta turn into a bathtub, I gotta get outta here!"

It's pretty cute watching em on actual dirt. Especially with a young'n, the little ones figure it out pretty quick. Somewhat accidentally, just (largely) by instinct!