At best, Signs was a very beige attempt at the then hot topic of alien invasion noughties movies. It was largely overshadowed by the reimagining of War Of The Worlds two years after its release, and while that film is also somewhat flawed, at least they attempt to explain why the aliens begin to die out. Here, however, we have aliens who have decided to make a full scale invasion... of a reverend's farm house. After over an hour of suspense and build up, Mel Gibson finally decides to explore his invaded house, finds one of the creatures relaxing in his living room and promptly tells little brother Joaquin Phoenix to "swing away" at its face with a baseball bat. Understandably, this makes the alien less than pleased, though vitally, it doesn't seem to do any damage, until teamed up with a simple glass of tepid water, which basically acts like acid and kills it. The key question is just how the alien managed to get as far as the surface without dying in crippling agony, as whilst we're not exactly merpeople, our planet is fairly plentiful in the whole atmosphere department when it comes to water. Not only is it a ridiculous weakness to have, but even as far as a Mel Gibson/M. Night Shyamalan/aliens movie will be sketchy on the facts, it just makes no scientific sense in the slightest.
