Unusual interference
It's an experiment someone tried a long time ago to teach animals to fly and it got a little out of hand.

NORAD has been tracking the repercussions of this experiment for the past 60 years and as far as they can tell the main side effects have been people breaking out in laughter and cheer.

There was a brief scare in 1993 when a slightly confused imposter tried the same experiment, but luckily this was quickly remedied.