I have a burr-type coffee grinder, and when it operates it naturally creates a bit of a potential difference (voltage) in the mechanism, which manifests as static electricity. Not much...not even enough to feel if I ground the machine with my body. But definitely enough to affect the tiny bits of coffee particles, so when I open the bin after I grind a batch, a tiny amount of coffee grind gets distributed all over the place by the voltage. Well, not really all over the place, just on the counter in front of the plastic collection bin.

The counter is granite. Black granite. The coffee grounds are blackish and tiny, so they are impossible to see. But I KNOW THEY ARE THERE!