J-Cut editing joke that no one seems to pick up on.
When Cindy is researching the cursed video, she stares at a photograph of a lighthouse and a foghorn sound effect blares loudly as the lead-in to the next scene at the actual lighthouse. The thing that makes it funny is the split second before the visual cut to the lighthouse, we see Cindy jump and react in fear to the foghorn sound from the next scene.
It's one of those little extra jokes that makes "Scary Movie 3" a lot like the first "Scary Movie" (and "the Naked Gun" and "Airplane!", for that matter). It's not perfect, but it's a big step back up from the 2nd Scary Movie, and the last couple.