The Hoovers get pulled over because the van's horn won't stop beeping. (Which, btw, made me laugh harder than anything else in the movie.)
Naturally everyone in the van freaks out. Because carrying a corpse in your trunk an activity that's embraced by the law. But the cop is so focused on the porn he finds that he doesn't notice much else...
FROM THE SCRIPT:
Richard watches McCleary walk around the back of the bus. He closes his eyes. McCleary opens the trunk.
Officer McCleary:
"Whoa! Goddamn!!"
Richard opens his eyes, shakes his head -- this is the end.
Officer McCleary:
"Sir, would you come here?"
As Richard plays along (in terror) with the horny police officer he says, randomly, "Sweet sweetness." I didn't see "Sweet sweetness" in the original script -- should we thank Mr. Kinnear for his improvisational skills?
I sort of missed what they were pulled over for in the first place...BUNS AND AMMO! HA!