Having cocked up quite a few times and touched something I shouldn't as an electrician's mate a good few years ago, part of me doesn't believe what he said he did could have had the effect reported. I'm not, and most likely never will be, an expert.... but I've had enough shocks to know that if there's a properly-working RCD on that circuit, you get a jiggle and say a few naughty words then the supply gets knocked out and everyone has a good laugh about it on teabreak.
I also doubt the muscle lock-up thing... for AC anyway (I always thought it was HVDC that did that, though I welcome any corrections!). Again only going on my own experience, a mains AC shock felt like intense vibration together with something like a cross between a nettle sting and hitting your funny bone, then jerking away from it. Not something I'd do on purpose, but with functioning RCDs/RCBOs on the line, not the end of the world and certainly not video-worthy.
That said, I do love my retro computing porn, so have subscribed to the chap's channel anyway!
EDIT: In case it sounded too much like I was making light of a potentially serious hazard, I did (eventually) learn, and get some proper 1kv insulated gloves for work that required things to be tested live.