To get you in the Christmas spirit, Source Filmmaker Harry101UK has put together a Portal-themed cover of Mykola Leontovych and Peter J. Wilhousky's Carol of the Bells.
The turrets - including the Animal King - break into song to celebrate Christmas and perhaps give thanks for the subjects willing to put themselves through all sorts of tests in the name of science. There are plenty of references to the Portal series in this three minute video, and of course it's full of references to firing bullets and neurotoxins. Those turrets never change!
Harry 'Harry101UK' Callaghan did the voices and the music himself, while August 'Rantis' Loolam provided the turret rigs.
Carol of the Turrets is available on Bandcamp.