How many people have seen a movie where there was an annoying piece of hair flapping around in the corner of the screen for the entire show? Well, that's exactly what it is. Between shows, the projectionist cleans out the projector head with a small paintbrush. The hair you're seeing probably fell off the brush during cleaning and wasn't noticed until the film started.
Many times, the edge of the screen will look like its growing a mustache. The problem here is a dirty or misaligned aperture plate, which is used to crop the edge of the picture. Sometimes a projectionist will be able to adjust it while the show is running, other times maybe not. If a theatre has this problem, I recommend that you complain. Because, its very likely that the projectionist doesn't know, or can't fix the problem, and if you act angry enough, you just might get some passes.
Another thing many of you may have already learned from the movie fight club is the term "cigarette burns"ÃÂ can any of you tell me what they do? They signify the end of a reel and the beginning of another. Another thing to look for at the end of a reel is dirt on the film. Dirt can appear as little black or white flecks on the screen. The dirt usually finds its way there when the movie is being assembled.