In reply to TobyA:
Here Toby
Unblocking a rope that is jammed behind the cam
In certain specific cases (for example, assisting the climber in regaining a high point after a fall, GRIGRI fixed on a carabiner attached to two points, rope climbing, etc.), the rope can become jammed behind the cam.
Don’t worry: this jamming does not damage the rope. Our internal testing shows that even with the smallest diameters, the rope remains intact, even if the climber falls. Note also that even with the rope in this position, the cam functions normally and the climber’s fall will be arrested.
Unjamming the rope is simple. Always hold the braking side of the rope when performing this action. If the rope is not under tension, push on the side of the device to reposition the climber side of the rope in the cam groove. If the rope is already under tension, simply pull on the braking side of the rope.
http://www.petzl.com/en/outdoor/grigri-experience#GE-coincement