Keywords are inclusive, so the more keywords you put in, the less lines you'll find.
You can specifically ask for a keyword to not exist by prefixing it with !.
For example, searching for "mouse !cheese milk" would find lines that contain both mouse and milk but not cheese.

[050614 02:06] f64d8, Peanut: *peeks*

[050614 05:07] abc8f, Ang: Wow, Valor's still around, that's interesting.

[050614 23:53] 5665f, Peanut: hmmm

[050616 05:07] 5cfd2, Billy: *urinates all over the city* Now I'm done! Ha!

[050617 05:29] 7977f, Peanut: *drops a Nerf nuclear bomb on the city and walks away, wiping her hands clean* There, that should do it.