There's a reason I put quotes around the word “slashes” up there – the Russian science teacher shown in this freaky clip didn't go all Jigsaw on her students and invite them to "play a game" or anything. This is actually a pretty cool and harmless (as far as I can tell) experiment in chemistry that had the class shrieking... and laughing.
The knife (which has no edge) is dipped in one solution, while the student's arm is swabbed with another. When the two are combined, the resulting chemical reaction creates a shockingly realistic bloody red trail.
So where were the teachers like this when I was trying desperately to stay awake in my high school Chemistry lab?