Juno, a beluga whale in a Connecticut aquarium, is known for his lively interactions with visitors - sometimes he gets aggressive, but other times he bobs to a mariachi beat, as you can see here. It's hard to say what we're witnessing, but it certainly seems like Juno is imitating the motions of the musicians as they play. Hopefully that's because he likes the music, and not because he's making fun of them or plotting their deaths.

(Spotted on Scuttlefishthanks, Blam!)