Why use fake blood when there’s so much real blood all over the place?

I’m watching/listening to the director’s commentary track of The Exorcist: The Version You’ve Never Seen. Among the interesting info is the fact that the opening scenes of the film were shot in and around Mosul, Iraq. Mosul, of course, is home to MO’s favorite medium infantry brigade.

William Friedkin recalled that Iraq was ruled by the Baathists, but not by Saddam Hussein, when the film was shot, which must have been in 1971 or 1972. He noted that the United States did not have diplomatic relations with Iraq at the time and that he used a British film crew and that they were allowed to film on two conditions: That they teach an Iraqi crew how to operate the film equipment and that they teach them how to make “film blood.”