I think I've mentioned this elsewhere on this forum, but I can't find it, so I'll post it again:
In an old edition of American Caving Accidents there is a first-person account by a guy who had a bizarre accident when on a solo trip.
It seems that he was prusiking up a ~70-feet entrance pitch using the Texas Prusik, which is a little bit like the Frog System but which uses a jammer to a sit-harness and another to foot-loops, which is relatively short and is installed on the rope below the harness-jammer. When he was nearly at the top of the pitch:
‘My [harness] karabiner flexed and came undone; I tipped upside-down, and for a short time hung there in my foot-loops, before my feet slipped out and I fell ~65 feet to the bottom of the pitch. When I came to, I thought I’d broken my neck.’. (He hadn’t, fortunately.)
Well, there was a pile of branches and stuff at the bottom of the shaft that cushioned his fall. By the half-light filtering down the shaft (his lamp being broken) he managed to cobble together some sort of rope-climbing system and get out.
What could he deduce from this? Well, ‘My karabiner had failed on two previous occasions, (my italics) but I had a sentimental attachment to it’ (pity it wasn’t reciprocated) ‘so I guess I’d better get a new krab. Also, had I had “chicken loops” round my ankles, I’d have hung upside down until I could sort out the problem.’