Science Marches On: Wells states that the changes to the animals are the result of various surgical techniques. Later adaptations of the same story state that genetic engineering is responsible for altering the animals.
Technology Marches On: While most adaptions of the story uses genetic engineering for Moreau's creations, the original novel actually uses vivisection, since it predates the discovery of genetics and DNA. Hence the House of Pain location in the novel, as the surgeries Moreau performs on his unwilling experiments are both unnatural and incredibly painful for the subjects.
Executive Meddling / Troubled Production: Hoo boy, did this one go through hell getting to the screen (director changes, prima donna actors making things difficult, typhoons hitting the set), and the final result shows how bad it was. It was the subject of a 2014 documentary, Lost Soul: The Doomed Journey of Richard Stanley’s Island of Dr. Moreau, which only scratched the surface as to how insane things got. This will probably go down in history as a rare example of a film adaptation that turned out to be less interesting than both the book that inspired it and the production that went into it!
Old Shame: David Thewlis had such a horrible time doing this he skipped the premiere and vowed to never watch the movie. Fairuza Balk had grown close to Richard Stanley during the pre-production. When Stanley was fired, Balk attempted to leave the production; she only continued out of contractual obligation and is not proud of the film.
The Other Marty: Rob Morrow was originally cast as Edward, but quit when Richard Stanley was fired. He was replaced by David Thewlis, who, ironically, was one of the actors Stanley wanted but couldn't get.
One scene has Moreau wearing an ice bucket on his head, because Brando showed up with it and no one asked him to take it off.
Majai, Moreau's Mini Mook, was Nelson de la Rosa. The production hired him because of his 2'4" height to play a fetal creature. What the producers didn't know was that de la Rosa was famous in South America. Brando met him on the set, and immediately took a liking to him, replacing Daniel Rigney's The Dragon role with de la Rosa, expanding his original role as background.