In Razorwire, a magician has a spectator come on stage and examine a frame of barbwire. The spectator can closely examine the wire to make sure that it doesn't come apart (it won't). Also, the magician can show that the barbwire is sharp by popping a balloon on it.
The magician stands behind the frame of barbwire and raises a cloth in front of him with the top of the frame still visible. He takes a step forward and lowers the cloth revealing that he has passed through the barrier unscathed, but his T-shirt is now ripped from the passage.