Keeping in line with Google's Let it snow feature where your results page fogs up when you search the phrase, YouTube now has a little snow button on some of its videos that allows you to populate them with accumulating snowflakes.
I've searched around YouTube, and found that the snow button is only available on some videos. I stumbled across it while viewing the Happy Holidays video from the Android team.
The button appears on the bottom right-hand side of the video box. When you press it, varied snowflakes begin to fall from the top of the video. If you pause a video, the snowflakes keep falling and will accumulate on the bottom. You can also use your mouse to disrupt the snowflakes.
Check it out on this video of a frog playing on a touchscreen:
I hope this cool little feature sticks around for awhile. If the snow button begins to appear on more videos, I can only imagine the hilarious juxtaposition of making it snow while Mr. Blonde cuts that cop's ear off in Reservoir Dogs.