Julia Roberts auditioned for the role of Dana Barrett, but it was Sigourney Weaver who attracted the filmmakers' attention. There was resistance to casting her because of the generally serious roles she played in "Alien" (1979) and "The Year of Living Dangerously" (1982). Weaver revealed her comedic background, developed at the Yale School of Drama, and began walking on all fours and howling like a dog. It was her suggestion Dana become possessed by the demonic dog, Zuul. Reitman said this solved issues with the last act by giving the characters personal stakes in the events. Weaver also changed the role from a model to a musician, saying she can be kind of strict, but "you know she has a soul because she plays the cello."