The production spent nearly $1 million on a life-sized replica of a giant octopus, which promptly sank when it was put in the water.
Henry Fonda filmed his scenes in one day. Fonda had just had a pacemaker fitted, and couldn't do anything too strenuous. All his scenes are fairly static, mostly talking on a telephone.
The film's distributor offered theaters a promotional poster that listed several points about octopuses including the fact that they can reach sizes of over 38 feet from arm to arm.
Although this was an entirely Italian production, it was shot in California.
Trailer narrated by Percy Rodrigues. The movie was sold as an alternate take on Jaws, and bringing in Rodriguez, most famous for narrating all Jaws trailers, was part of this campaign.