If you were under the impression that pressing the spacebar on YouTube pauses the video, you are mistaken. In fact pressing the spacebar while watching a YouTube video, makes the screen jump to the comments section.
So which key can pause the video in YouTube?
YouTube user, GradeAUnderA did some plain old style detective work and found out that pressing K while watching the YouTube video pauses it. He also found that pressing J will take the YouTube video back 10 seconds and similarly pressing L will take it 10 seconds forwards.
GradeAUnderA made a YouTube video to showcase his findings and the video has gone viral with around 600K + views. In fact, it featured on the front page of Reddit through Sunday.