Signs. A fun movie but come on (don’t read further if you haven’t seen yet). The aliens have the technology to travel interstellar space but have no weaponry, body armor, and can’t identify beforehand that an incredibly common earthly substance will put their invasion at risk? And humanity has a problem fighting off aliens who have no weaponry, body armor, or hand to hand combat ability? Ok I am overanalyzing. My kids liked it. I had fun too.