Oversized helium balloons were first introduced during the "Dark Side of the Moon" tours, but in 1975, this element began to play a central part of the live show. For the U.S. leg of the 1975 tour, a pyramid shaped dirigible was floated above the stage. It proved unstable in windy conditions and blew into the crowd, which tore it into pieces for souvenirs. The trademark giant pig was brought in for "Animals" in 1977, floating over the audience, as well as a grotesque 'Nuclear Family', a refrigerator filled with snakes, a television and a Cadillac. In some shows, an envelope of propane gas was put inside the pig, causing it to explode. The inflatables reached their peak in 1980–1981 during "The Wall" shows, in which several of the characters from the album were brought to life in the form of fully mobile, giant string puppets with menacing spotlights for eyes, taking the traditional balloons to a new level. The characters were designed by the notable satirical artist, Gerald Scarfe.