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.
Billing Displacement: Protagonist Edward Douglas (David Thewlis) is nowhere in the cover, unlike both Moreau himself (Marlon Brando) and Dr. Montgomery (Val Kilmer).
Executive Meddling / Troubled Production: The 1996 version was rocked by this, kicking off when director and screenwriter Richard Stanley was canned after four days of shooting. The documentary Lost Soul: The Doomed Journey of Richard Stanley's Island of Dr. Moreau covered the madness.
Stanley was replaced by the veteran John Frankenheimer. However, most of the cast and crew hated working with him, especially Fairuza Balk, whom he bullied during the entire production. He was hired to control Val Kilmer and Marlon Brando's egos - and failed miserably; The two actors (who while already infamous for erratic behavior were both in a Creator Breakdown) refused to work together, resulting in scenes where little made sense. Brando even had Daniel Rigney's role replaced by Nelson de la Rosa (who would go on to inspire Mini-Me.)
The extras, however, loved the extended production, having almost nightly parties filled with booze and drugs.
Richard Stanley went off into the woods and started becoming a Granola Guy and started practicing witchcraft. Two crewmembers found him and had him sneak onto the set as one of the extras, and was filmed in a few scenes. Keep in mind, part of his severance pay was that he not come within 100 meters of the production!
Old Shame: David Thewlis had such a horrible time doing this he skipped the premiere and vowed to never watch the movie.
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.