Hats Off (lost silent Laurel and Hardy film; 1927)
Hats Off is a silent two-reel Laurel and Hardy short film from 1927, the tenth in order of production. The film involved Laurel and Hardy as salesman attempting to sell a washing machine, but failing each time. The two running gags of the short are Stan and Oliver always falling down a large flight of steps and having to carry back the machine to the top. Hat-switching, another running joke in their films, was also prevalent here, as the title might indicate.
The movie was remade by Laurel and Hardy into a talkie called The Music Box, revolving around a piano instead of a keyboard and using similar gags.
Despite the film's great success among critics and public, it vanished after its last screening in Germany in 1930. There have been several unconfirmed rumours of sightings of the movie in the 50's, but none have been confirmed, and no prints have been found. Laurel and Hardy historian Randy Skretvedt dubbed Hats Off "The Holy Grail of Laurel and Hardy movies." 
Lake, an early TV film distributor, listed Hats Off as available for TV bookings. This was later proven to be a mistake, as he used a list of all shorts ever created rather than what was accessible to them.
All that has survived is the original script, several stills, and posters of the film, but no video footage is known to exist. A reconstruction of the film has been made based on the script and surviving stills from the film.