20 Minutes

Prague, 7 December 1975

In a basement room, I placed a long iron rod on the ground, perpendicular to the wall. I screwed one end to the floor and tied a large knife to the other end whose tip touched the wall. I asked a member of the audience to assist me. I asked him to sit on a wooden board placed on the rod and when he saw that I wasn't concentrating, to move up any distance he chose. I set the clock at 20 minutes without him knowing about this limit, and sat down between the knife and the wall. The clock didn't work properly. I stopped the action after 44 minutes.