You know that part in the movie "Harry Potter and the Prisoner of Azkaban" where Aunt Marge blows up like a Macy's parade balloon and her buttons pop and her dress rises up so you can see her garters and then she floats up out of her chair and out the door and up into the sky?

It's basically a sight gag, which means that someone like Dave Sarle — blind since a shooting accident 26 years ago — has no idea what's going on.

In fact, much of what transpires at the movies is largely visual. Close your eyes during the trailers and you'll hear lots of whooshing and thudding but no mention, for example, that the movie being previewed is called "Catwoman."

Sarle used to love the movies. Before the accident, which happened when he was 15, Sarle practically lived at the movie theater. After the accident, the movies proved too frustrating. Either his friends would forget to give him a running account of what was happening in back of the dialogue, or they would tell him and everyone else in the theater would get annoyed. "Shhhhh," people would say in his general direction. "What, are you blind or something?"

Now, though, going to the movies is fun again, thanks to a system called Descriptive Video Service, recently installed at the Megaplex 12 Theatres at The Gateway. Although DVS is available in other theaters in the United States, this is the first use of the system in Utah. The next closest DVS is in Arizona, says Sarle, a member and volunteer with the National Federation of the Blind of Utah.

DVS provides an audio description of a movie's action and scenery via a running narrative seamlessly inserted in the spaces between dialogue. The narrative comes through a special headset; the dialogue can still be heard on the theater's sound system.

Yesterday, Sarle watched "Harry Potter and the Prisoner of Azkaban" for the fourth time. As he put on his headset and settled in with his large soft drink, the Warner Brothers logo came on the screen and a soothing British voice began setting the scene: "Behind the shield, a faint light flickers on and off from inside a house."

DVS works like this, explains Megaplex 12 projection supervisor Mike Renlund: The audio track is synchronized to match up with certain frames on the film, according to the time code on both the film and audio. The system costs about $6,000 per auditorium to install and is currently in only one of the 12 theaters at The Gateway megaplex.

Renlund says that the theaters are also looking at installing a $5,000 "rear-window captioning" system for hearing-impaired moviegoers. With this system, a viewer can read dialogue on a 5-by-10-inch piece of smoky Plexiglas that reflects a read-out display on the theater's back wall.