Not long ago, a man in an aviator cap began appearing on screens around the world. A slender fellow in a teal short-suit, he grooves against computer-generated backdrops—a pirate ship, a gemstone mine, an island guarded by sinister flamingoes—inviting his viewers, with intense cheerfulness, to mimic his dance moves. “Hey!” he calls out to the kids watching on YouTube. “You wanna shrink down with me and dance like some different insects?” Electronic beats throb as he swipes groceries across a