Steven Spielberg devised the three trials that guard the Grail. For the first, the blades under which Indiana ducks like a penitent man were a mix of practical and miniature blades created by Gibbs and Industrial Light & Magic. For the second trial, in which Indiana spells "Iehova" on stable stepping stones, it was intended to have a tarantula crawl up Indiana after he mistakenly steps on "J". This was filmed and deemed unsatisfactory, so Industrial Light & Magic filmed a stuntman hanging through a hole that appears in the floor, thirty feet above a cavern. As this was dark, it did not matter that the matte painting and models were rushed late in production. The tarantula version is used in a comic book adaptation of the movie. The third trial, the leap of faith that Indiana makes over an apparently impassable ravine after discovering a bridge hidden by forced perspective, was created with a model bridge and painted backgrounds. This was cheaper than building a full-size set. A puppet of Harrison Ford was used to create a shadow on the nine-foot-tall by thirteen-foot-wide model, because Ford had filmed the scene against bluescreen, which did not incorporate the shaft of light from the entrance.