In Fight Club Tyler Durden gets several tapes of film together to make one long reel. Some technicalities get explained in the process. And he has fun inserting some random image in between. I don't think so while I'm reading Palahniuk's book, but:
Does the movie explain how sound & image are attached?
To more precisely answer the question: if you look at a frame of 35mm film that is screened in a theater, it has a optical channel on the side of the frame - it is sound encoded as a wavy line, printed right on the film. You don't need to do anything special to get the sound with the frame when you splice it into something else.
UPDATE: Based on what Tyler is working with, in addition to the era, the sound will be on the film as optical only, without having to sync the sound.
This is the type of conversation that gives Art Directors nightmares!
Source: I was friends with several professional projectionists at the time (1980s-1990s) and edited on film in the late 1990s
The images come from other movies(often pornographic films). He simply cuts pieces of film from the reels that he wants and splices them in where he wants them (usually between reels of the main film, where it is easiest because he doesn't have to cut the reels of the main film). It isn't explained any more than using a doorknob on the way from one room to another is explained. He has access to the material and the tools needed because he works as a projectionist.
There is some noticeable sound, as he is only adding a few frames, too few to notice a break, consciously, but enough to register subconsciously. At about 29 or 58 Frames per Second (FPS), 6 frames would be a blink. He splices on a frame with a sound channel, almost literally cutting and pasting it in between the regular film, played by the projection system in sync. The film has video and audio on the same cellophane reel, side by side, read by different parts of the projection system. That's how movie projectors work.
