Certain concepts about dinosaurs, like the theory they evolved into birds and had very little in common with lizards, were followed. This prompted the removal of the raptors' flicking tongues in Tippett's early animatics, as Horner complained it was implausible. Winston's department created fully detailed models of the dinosaurs before molding latex skins, which were fitted over complex robotics. Tippett created stop-motion animatics of the raptors in the kitchen and the "Tyrannosaurus" attacking the car. Despite go motion's attempts at motion blurs, Spielberg found the end results unsatisfactory for a live-action feature film. Muren told Spielberg he thought the dinosaurs could be built using computer-generated imagery; the director asked him to prove it. ILM animators Mark Dippé and Steve Williams developed a computer-generated walk cycle for the "T. rex" skeleton and were approved to do more. When Spielberg and Tippett saw an animatic of the "T. rex" chasing a herd of "Gallimimus", Spielberg said, "You're out of a job," to which Tippett replied, "Don't you mean extinct?" Spielberg later injected this exchange into the script, as a conversation between Malcolm and Grant. Although no go motion was used, Tippett and his animators were still used by the production to supervise dinosaur movement. Tippett acted as a consultant for dinosaur anatomy, and his stop motion animators were re-trained as computer animators. The animatics made by Tippett's team were also used, along with the storyboards, as a reference for what would be shot during the action sequences. ILM's artists were sent on private tours to the local animal park, so they could study large animals — rhinos, elephants, alligators, and giraffes — up close. They also took mime classes to aid in understanding movements. Universal paid Crichton a further $500,000 to adapt his own novel, which he had finished by the time Spielberg was filming "Hook". Crichton noted that because the book was "fairly long" his script had about 10 to 20 percent of the novel's content; scenes were dropped for budgetary and practical reasons, and the violence was toned down. Malia Scotch Marmo began a script rewrite in October 1991 over a five-month period, merging Ian Malcolm with Alan Grant. Spielberg wanted another writer to rework the script, so Universal president Casey Silver recommended David Koepp, co-writer of "Death Becomes Her".