In the Swimming Pool, Palm Beach, Florida (1905)
The title tells you what pretty much happens in this film but there's a trick. The film starts off with people jumping off a diving board into a pool as well as jumping from a second story into the pool. Then the movie puts the footage in reverse and we see them jumping backwards. This type of "trick" film was done as early as the late 1890s but the biggest difference between those and this film is that this one lasts nearly four minutes and it becomes very boring very quickly. The cinematography is weak to say the least and the trick itself is just so obvious that I'm sure people in 1905 felt cheated by this.