One can only imagine the faces of the guards outside Arthur's room listening to this exchange. Merlin was holding onto a rope that allowed Arthur to escape from his room. Unfortunately, the rope wasn't long enough and Merlin was forced to drop Arthur halfway down.
Arthur: (muffled) What are you doing...the rope!
Merlin: panicking) THERE IS NO MORE ROPE!
Arthur: (straining) Merlin...
Merlin: (groaning) Oh...I don't know if I can hold on any longer!
Arthur: (even more strained) ...don't let go of the rope!
(Merlin groans until there's a startled shout and then a thump)