How true to life are the events portrayed in "The Exorcist"?

A: "The Exorcist", written by William Peter Blattey, is based upon an actual case of demonic possession, & the subsequent exorcism, of a fourteen-year-old boy, which took place in the U.S. in 1949. Some of the events are documented as having actually occurred, such as writing appearing on the boy's flesh, & his ability (while under possession) of speaking in foreign languages. In the actual case, the exorcism eventually proved successful, & the boy went on to live a normal, healthy life. None of the priests involved actually died as the result of the exorcism, or became possessed themselves, although one priest did suffer a broken nose. Some of the more bizarre phenomena portrayed in both the book & the movie never actually happened, such as the head spinning & the "spider walk". Some of the events portrayed in "The Exorcist", however, when taken in context, are actually supposed to be telepathically projected into the minds of certain characters.

One thing I should mention about "The Exorcist" which happens to be very true to life, is that these types of parasitic, hostile entities are often initially & inadvertently "invited" in to begin oppressing certain individuals, through the use of a Ouija board.