I still haven't seen Signs, so I've been only lightly skimming this thread lately. Some of SLL's comments about "traditional" science fiction aliens reminded me of a science fiction novel by Larry Niven and Jerry Pournelle: Footfall . Not to give away the way the story unfolds, but it looks at the scenario of a species achieving space travel that isn't really as well-evolved a tool-user and intellectual as the human race, and that species stumbling across Earth. It's the only book I know of that has drawf elephant paratroopers invading Kansas.

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