What was used to simulate the green vomit in "The Exorcist"?

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One surefire way to kill Christmas cheer is lining up in the cold to watch children get possessed and projectile vomit, and that's exactly what audiences did when "The Exorcist" opened on December 26, 1973. The scene where possessed Regan spews green bile all over Father Karras became instantly iconic (and one of many reasons why moviegoers ended up leaving early). What was used to simulate the green vomit in "The Exorcist"?



