existent  jolt. Desilu wanted absolute realism, so the set containing the  trains curtained berths and a hallway leading to the door with the  emergency brake next to it was built in a box frame that contained a  spring mechanism that was in turn triggered by the emergency brake  itself. When Lucille pulled the handle of the brake, it released a  metal spring that caused the entire set to lurch forward in a  movement that often brought the actors to their knees; thereby  accurately simulating an emergency braking of a trains movement.  This is demonstrated in the special features section of the DVD.