The kid starts bobbing his head as soon as music plays.
Tips
history
Lu Xun in 《二心集》 describes bad translations being read 摇头晃脑, mocking the head-wagging rhythm of scholars savoring their own words.
culture
Classic image of old-style scholars reciting the classics, lost in the sound of their own chanting. Now often slightly mocking — suggests pompous self-enjoyment.