Gina Gershon had been originally offered the role of Sharla almost 20 years previously when the script was for a play, but she turned it down because she could not imagine performing the infamous chicken-leg scene "eight times a week" on stage.
The film was released theatrically with an NC-17 rating by the MPAA for "graphic aberrant content involving violence and sexuality, and a scene of brutality" but was edited down to an R rating for the home video release so that the DVD and Blu-ray could be sold in certain stores. The reason for the R rating given by the MPAA was for "strong and disturbing violence, sexuality, graphic nudity, drug use and language".
In one scene Dottie asks if Joe is a detective like Magnum PI. Matthew McConaughey was in the running for playing Magnum PI in a big budget movie remake of the series in 2007, as of 2012 the project is dead in the water.
Director William Friedkin was shocked when he found out that the film was given the NC-17 rating and refused to alter the film for fear that any cut or edit would take away from the filthiness of the film. It was released theatrically with the NC-17 rating only to have an edited R rated version released for certain retailers to carry when it was released on DVD and Blu-Ray.
The trivia item below may give away important plot points.
Although they are the characters who kickstart the whole story, neither Rex nor Adele are ever seen in any meaningful context: Adele is only seen briefly after she is murdered and Rex is seen briefly in two scenes with his face slightly obscured. Neither are heard speaking.