New films 'RV,' 'United 93' and 'Stick It' take the top three spots at the box office.
Horror-movie spoof knocked out of #1 by the real thing.
Here's a look at why the horror spoof succeeded where others have failed.
Spoof earned $41 million, knocking 'Ice Age: The Meltdown' to #2.
It's business as usual for spoof sequel, which takes on 'The Village,' 'Million Dollar Baby.'
'Scary Movie 4' brings to mind some classics of that tricky genre — the funny scary flick.