I'm not 100% sure about this because I've never used a tens unit that used velcro to attach the electrodes, only the sticky kind. But those, if you don't get them "tight enough (complete contact with the skin), or if they loosen because the sticky stuff doesn't stick, they will cause electrical burns from, I think, arcs of electricity. So I *think* the reference to them in the beginning of the comic and short story

where Kat thinks to herself that having them loose will just cause a buzzing sensation that is not helpful but not harmful
might be factually incorrect--or I suppose we could chalk it up to literary license. I'd ask my own personal nurse/burn victim (lol ... I try to be a nice wife but don't always succeed), but he's asleep currently.

Anyone got any input on this? GNTLGNT? Ally? Aggie?