Arnold Schwarzenegger was injured on the set of Terminator 3 one day while filming a wild chase scene involving a construction crane and a fire truck. The first wall, he was told, was a breakaway wall: "You'll crash right through it, no problem." "'Ok,' I said, 'let's do it,'" Schwarzenegger recalled. "I hit the wall and slid right down it." Technicians, it seems, had forgotten to take out a rigid structural beam.
["Sometimes there are dangerous scenes that don't even look dangerous," Schwarzenegger once remarked. "I remember once when I did this diving scene in The 6th Day, in Vancouver; all of a sudden I got lost under the tank of a boat, under the water. When I came up for air, I hit the bottom [of the boat], and I couldn't get out." (He was rescued by another diver.)]