Signs has got to be one of the most ridiculous movies ever (except maybe for The Last Airbender, or After Earth)...
Indeed, those aliens failed to notice water on our planet, even though it's pretty much the only chemical compound clearly visible from outer frikkin' space!
-Throughout the movie, the alien creatures are seen jumping on and off roofs with no trouble. But when one of those aliens is trapped in a room, he (or she?) is unable to escape...so a mind smart enough to travel the galaxy, combined with a body strong enough to jump ten feet into the air, is incapable of forcing a door!?
-Mel Gibson plays a priest who lost his faith...and what happens to make him a priest again? An alien invasion!? I dunno, but I think an alien invasion would pretty much moot the entire bible, starting with Genesis: 'In the beginning god created heaven and earth...and other planets, with other earthlike things (...) And on the sixth day he created man...and aliens.' Good luck working that into your sermon.
-Alien poison only works when it enters your lungs...thank god (pun intended) for asthma...and for the fact that this poisonous substance only has effect on your lungs and not a single other organ.
-So them aliens are allergic to water...could that be why it never rained in that movie?
-In the beginning of the movie, a dog got killed by a fork. A fork!? Can you really kill a dog with a fork? I know it's unethical to try, but seriously!?
-Oh by the way...I know we don't fully understand evolution yet, but isn't water like a necessary ingredient to harbor life? Didn't life start in water? And even if it didn't on some other planet, why didn't they just invade Mars? Hell, I would've given them the moon if they asked politely.
-Why crop circles? I know they were a thing a few decades ago, but why would aliens need crop circles? They've traveled the universe. Don't they have more advanced methods of communication?
-Why didn't the aliens carry any weapons? Did they really not prepare their invasion at all? A quick study on mankind would have taught them mankind likes to shoot at stuff we don't like.
-Btw...what's the point of jumping on roofs? If we ever invade another planet, will us humans start jumping on the houses of other species for no apparent reason?