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.

Keywords:
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2 lines found
[050701 04:49] 26942, darkEcho: ~peeks into times past~
[050702 01:46] cc6ec, Peanut: ((peers))