Browning was paid $10,000 to direct The Unholy Three.

The film rights to Robbins's book had previously been purchased by Clarence Brown in 1919, when he was working as an editor. But Brown's mentor, director Maurice Tourneur, persuaded him to seek a more marketable property instead.

Chaney based his performance as Echo upon an actual criminal. "August Vollmer, police chief and criminologist, told me of a hotel thief he had arrested who was also a physician," Chaney said. "Incidentally, I understand his man reformed, and, after serving his term and taking his medicine, has rehabilitated himself in society."

As a gag, and a means of testing their disguises, Chaney and Earles visited the MGM Wardrobe Department as Mrs. O'Grady and baby Willie, and requested a diaper change. When the costumer was unpinning Earles's pants, he cried, "You will like hell, madam! Not this baby!"

One day, McLaglen filled one of Tweedledee's baby bottles with Scotch. "You should have seen Lon in a wig and false front and big false keister sucking on that nipple!" Earles said, "You would've died laughing."

In the novel, Echo is effeminate, and disguises himself as a young woman. This "beautiful girlish face" was one face that Chaney was unable to conjure from his makeup box, so it was decided that he would become "Granny" O'Grady instead.

The giant ape that unleashed his fury in the film's climax was actually a normal-sized chimpanzee that was filmed on miniature sets. In one scene, a child is substituted for Chaney, to enhance the optical illusion. The pressbook claimed it was a 1,400-pound gorilla. Browning played along and exaggerated the ferocity of the beast, "Every shot that was taken of this animal was taken at great personal risk and exacted an amount of patience that is hard to describe. We were in momentary dread that he would break from his cage and kill everybody connected with the taking of the scenes."

The total budget of The Unholy Three was $114,000. Its total worldwide gross was $704,000. MGM's profit was registered as $328,000.

Research compiled by Bret Wood

Sources:
The MGM Story
Classics of the Silent Screen: A Pictorial Treasury by Joe Franklin
The Horror People by John Brosnan
Dark Carnival: The Secret World of Tod Browning by David J. Skal & Elias Savada