I must admit, "The Exorcist" still scares me to this day. The gore, special effects and the religious undertones all scare the crap out of me. Despite the effects not working as well as others and it being removed completely from the original version of the film, the deleted spiderwalk scene is truly unsettling (both in the movie AND the book). It's definitely one of those images that's hard to erase from your mind.
The following is a clip of William Friedkin and Peter Blatty discussing the spiderwalk scene and how Chris must deal with the death of her friend and instantly see the horror of her daughter contorted and walking down the stairs. The interview also shows the page from the book describing the spider walk:
The actual stunt was performed by contortionist Linda R. Hager. The scene was cut because the effects did not work as well as others throughout the movie; visible wires could be seen suspending Hager in the backward arched position as she descended the stairs. The scene was featured in a BBC documentary, "The Fear of God: The Making of The Exorcist," which was included in the 25th Anniversary Special Edition DVD in 1998.
In the 2000 theatrical re-release entitled "Exorcist: The Version You've Never Seen" Friedkin used CGI effects to digitally remove the wires and the scene was reinstated back into the film. Other changes and additions in the new edition include digital effects of demonic faces and images of the statue, a digital effect of Regan's face morphing into the devil, new growls, additional lines and extended scenes.