Ray Harryhausen used stop-motion animation to create the various creatures in the film, including Calibos, his vulture, Pegasus, Bubo the mechanical owl, Dioskilos, Medusa, the scorpions and the Kraken. Harryhausen was also co-producer of the film, and retired from film-making shortly after it was released. Despite Bubo's similarities to the droid R2-D2 of the 1977 film Star Wars, Harryhausen claimed Bubo was created before Star Wars was released.[12] The BBFC, reviewing the film for certification in 1981, said Harryhausen's effects were well done and would give entertainment to audiences of all ages, but might appear a little "old hat" to those familiar with Star Wars and Superman.[2]