that day and he had "blinding headaches" for weeks afterwards, but continued working, having a well-known high threshold for physical pain. It was not until 1935 that a doctor spotted a callus over a fracture in Keaton's top vertebra in an X-ray. The doctor informed Keaton that he had broken his neck during the accident nine years earlier and not realized it. Keaton famously always performed his own stunts, and this was not the only accident on set. In another scene, the motorcycle Keaton was riding skidded and smashed into two cameras, knocking over Eddie Cline and throwing Keaton onto a nearby car. Sherlock Jr. was also Keaton's most complicated film for special optical effects and in-camera tricks. The film's most famous trick shot involves Keaton jumping into a small suitcase and disappearing. Keaton later said that it was an old vaudeville trick that his father had invented, and he later performed it on the Ed Sullivan Show in 1957, but never publicly revealed how he did it. The trick was accomplished with a trap door behind the suitcase and an actor lying horizontally with long clothes hiding his absent bottom torso, which then allowed the actor to smoothly fall forward and walk as though he had always been standing vertically. Keaton later said that they "spent an awful lot of time getting those scenes." Filming took four months, while typically it took Keaton two months to finish a feature film. The editing was also difficult and took longer than a typical Keaton film. Keaton later told film historian Kevin Brownlow "every cameraman in the business went to see that picture more than once trying to figure out how the hell we did some of that." Keaton depicted an early example of a film within a film in the dream sequence. Keaton's character leaves the projection room and goes down into the theater, then walks into the film being screened on the stage. Keaton later explained that this stunt was achieved through the use of lighting: "We built a stage with a big black cut-out screen. Then we built the front-row seats and orchestra pit. ... We lit the stage so it looked like a motion picture being projected on to a screen". Keaton's character is kicked out of the film a few times but finally manages to stay in, and is then depicted in a series of different scenes