Stop motion animator Willis O'Brien, who had worked on "The Ghost of Slumber Mountain" and "The Lost World", was again responsible for special effects in the 1933 monster movie "King Kong", which featured a climactic battle between the giant ape and a "Tyrannosaurus". The "Tyrannosaurus" model was made using a cast based on an early painting by Charles R. Knight. O'Brien stated that the battle between Kong and the "Tyrannosaurus" was one of the most technically difficult scenes in the film to animate. Many early films depicted "Tyrannosaurus" with an upright posture based on the current thinking of the time. Most of these films inaccurately portrayed the dinosaur with three prominent fingers on each hand like "Allosaurus" (though "Tyrannosaurus" had a third, vestigial finger, it would not have been noticeable at first glance); Walt Disney is reported to have informed dinosaur hunter Barnum Brown that "it looked better that way", and the creature was depicted as such as in the Igor Stravinsky's The Rite of Spring segment in the Walt Disney 1940 animated film "Fantasia". Since that time, "T. rex" has appeared in a great number of "monster" films and educational documentaries. One of the first appearances which portrayed a proper posture and anatomy of "Tyrannosaurus" is the 1984 short "Prehistoric Beast", fully conceived and made by Phil Tippett by means of his so-called go motion technique.