During the IDC for a practice run I drew the CESA. A staff instructor had set up a rope tied to a dock at 25 ft or so, attached to a float.
My turn came, I got set up on the rope and beckoned my 'student' to join me. When he did and we began the CESA I discovered rather quickly that the knot holding the rope to the dock had unravelled, leaving me and my pretend student struggling with our bouyancy.
I got that sorted out, then the knot holding the other end of the rope to the float unravelled, so another 20 feet of rope came down on my head, leaving me with the job of untangling myself.
As a nervous instructor candidate, I found it a bit difficult not to take all this personally. I found it even more difficult not to murder the staff instructor in question, who later claimed that he had done this on purpose in order to help us "train for unexpected scenarios".
Needless to say, when I actually do a CESA, I tie my own @#$! knots.