Jennifer Connelly had part of her finger bitten off by the chimpanzee in the final scene at the end of the film. She was rushed to the hospital and the finger was re-attached.
Jennifer Connelly said in an interview that she was bitten by the chimp in this film. Apperently during one scene the chimp kept turning around and Dario Argento, not wanting to film her behind, asked Connelly to place her hand on the animal to stop her from turning. But when she attempted to do so, the chimp became enraged and bit her; and then became very hostile toward Connelly for the rest of the film.
Director Dario Argento often cites this film as his personal favorite among his works.
The film was inspired to Dario Argento after he learned that insects are sometimes used during murder investigations.
The trained chimpanzee that plays Inga escaped into the woods at one point during shooting. After a few hours of searching she was found and returned to the set.
(at around 15 mins) The story Jennifer tells about her mother abandoning her was an actual story from Dario Argento's own childhood.
Most of the Italian and other non-English speaking actors/actresses actually dubbed their own voices into English for the USA and UK distribution.
The Patau Syndrome used in this movie is an actual syndrome, which is caused by a chromosomal abnormality.
The shots of the swarm of insects covering the exterior of the school, and later nearly blotting out the moon were achieved through visual effects. They dumped a bunch of coffee grounds in a tank of water, filmed it, then superimposed the new footage over existing background shots.
A sequel was going to go into production in 2001 but it was canceled due to Dario Argento's contract with Medusa.
The imagery, aesthetic and partial plot points of the film were used as inspiration for the 1995 survival horror video game Clock Tower. In the game, you play as a young woman named Jennifer Simpson who is trapped in a sprawling mansion estate with a psychotic, scissor-wielding deformed boy. The character Jennifer is clearly modeled after actress Jennifer Connelly's appearance in the film.
The larvae were created by placing vermiculite in water and adding liquid chocolate and essence of mint.
The painting hanging over Jennifer's bed is 'Village Landscape in Morning Light' by Caspar David Friedrich.