The fly touched down on Vice President Mike Pence's lustrous white hair midway through the vice-presidential debate on Wednesday night. For more than two minutes, it stayed put - a jarring black dot on millions of TV screens.

It begins with a few quick electric-yellow flashes at dusk, followed by about eight seconds of darkness. Then more flashes, and more darkness. As the night wears on, the blinking builds until hundreds of thousands of fireflies flicker their lamps in unison, then douse their bioluminescent flames and usher the forest back into black. A few long moments later, the whole silent spectacle starts anew.