Tod Browning wrote the story for "The Mystery of the Leaping Fish" while recovering from serious injuries in a 1915 auto accident. The crash killed his passenger, actor Elmer Booth.
According to Jeffrey Vance, Douglas Fairbanks hated the film and wanted to have it pulled from circulation.
That big expensive car used by the villain is a 1916 Winton Big Six Touring Car.
"Coke Ennyday" is a parody of the fictional detective Professor Craig Kennedy. Written by Arthur B. Reeve, the Craig Kennedy short stories were immensely popular at that time, appearing over eighty times in "Cosmopolitan" Magazine. Kennedy is a scientist-detective at Columbia University similar to Sherlock Holmes and Dr. Thorndyke. He uses his knowledge of chemistry and psychoanalysis to solve cases, and uses exotic (at the time) devices in his work such as lie detectors, gyroscopes, and portable seismographs.
Painted on the side of the wagon is "Sum Hop Laundry". A "Hop Head" was slang for a drug user, so that laundryman must have been Some Hop.