Well, it's possible that things got out of hand. I know there have been times I've been doing edgeplay with a lover that I actually became scared it was going to go too far. It's made me very careful about who I play edge games with and who I don't.
I mean, I know that as soon as my lover puts the duct tape over my nose she could slip & fall and knock herself out and I'd be toast. Slim odds, sure, but it could happen. You just have to be careful.