I did not believe it when I first heard of it either. The MIND = BLOWNpart is usually thrown in for suckers by trolls. Well, this time it was not a troll, and the easter egg was for real.
As neoconnor1111 says in his video‘s description, YouTube has a wierd [sic] secret. If you press and hold the left arrow key while playing a YouTube video, a small overlay pops up. What is this overlay? A game of Snake. It seems Google does like its retro gaming a lot.
This works on any video (obviously), and the best part is that you can keep playing the game while the video is being buffered (and played) in the background.
I believe this is where Buffering Boredom has met its match.