A pre-lap is a Scene Transition
where the sound from the scene transitions before the visuals do, so the sound of the second scene momentarily coincides with the visuals from the first scene.
Because the viewer will naturally try to connect what they are seeing with what they are hearing, it is often used to portray a logical connection between the two scenes.
This is also sometimes employed in comics by including speech from one scene as narration boxes over the preceding scene.
The reverse of this is the post-lap.
- The Graduate, where Dustin Hoffman is in the bottom of a pool but you hear him having a phone conversation with Mrs. Robinson in the following scene.
- Indiana Jones and the Last Crusade. As Indy is looking at a road sign leading to Berlin, the sound of drums is heard. As the scene changes to Berlin, the drums fade into parade music as Nazi soldiers march around and burn books.
- An interesting one in Star Wars: Episode I - The Phantom Menace: When Shmi overhears Qui-Gon discussing the implications of Anakin's impossibly high midi-chlorian count, Darth Maul's Sith chanting theme begins, serving as a lampshade on the conversation before transitioning to Maul's arrival.
- Lawrence of Arabia, where the sound of a train whistle is heard over the end of the previous scene. The Ur-Example and Trope Maker.
- Primer has a scene in which an ice machine is activated on a refrigerator, and a noise is heard. Said noise turns out to be construction equipment from the next scene, where the protagonists are trying to build a device in the garage.
- Rather bizarrely, considering the lowbrow humor of most of the movie, Scary Movie 3 actually directly parodies this rarely-noticed-or-discussed phenomenon during its parody of The Ring, with the main character reacting to a sudden boat horn piped in from the next scene. Not sure anybody else got it.
- eXistenZ post-laps Geller and Pikul's breathy make-out sounds over a dead amphibian that dangles from Ted Pikul's hand.
- Constantly used in EastEnders.
- Lost uses it often, particularly for transitioning to flashbacks in the early episodes, before the trademark "woosh" noise was added.
- Person of Interest uses this to move from scene to scene with the sounds of conversations overheard through telephones, recorders, and so forth, coupled with a visual transition pinpointing the next location and zooming in.
- In the Cracked video series "After Hours," David attempts to discuss with an unwilling Soren the immorality of cereal mascots. The two of them (three including Michael) are in the bathroom, and Soren is using the urinal. David is just standing behind him badgering. The scene ends with a sound resembling a public toilet flushing; it turns out to be Katie spraying whipped cream directly into her mouth.