In reply to saturn:
To expand on this as I may have been a bit flippant: was attempting Rhinoceros (E2 5c) on Haytor Low man with a mate; second pitch he teetered up the groove then fell off the exit. I held the fall, he was gutted wanted another go. I shouted that I had seen a puff of white as he came off, and would rather lower him to the ground. Once I did, the rope came away in his hands, granite crystal had cut right through a brand new rope. A very good argument for climbing with half ropes, although I'm still not sure if he would have stayed off the deck if that rope had been cut. Pretty sobering day!