Yes they definitely know the science behind it and do a good job making it entertaining.
Unless you wrap all your fingers in one hand around a neutral wire and the all fingers in the other hand around live, it's unlikely to get yourself killed from mains. And the neutral and live conductors must be something thick so that when your muscles contract, you should not be able to release your grip.
I have three phase machines in my home shop with plugs that have reversible pins. So to reverse the motor, you unplug the machine, reverse the two pins and then plug it back in. Every now and then I try to reverse the pins while 380V is still plugged in, and all that happens is a good scare and lots of cursing.