Wayfriend wrote:I think the plot hole is that an alien civilization with the technical capabilty of travelling interstellar distances to mow corn would maybe think raincoat.
It's still not a plot hole. For a start, the aliens were turned back - some killed - and they retreated. Their fleets left taking what they were after from the start - people. If every one of the aliens were killed, sure it's a massive blunder, but the water made them simply get into their craft and leave. They didn't neeed to don 'raincoats' for the fact that most places they attacked were not inundated with water-weilding citizens.
Wayfriend wrote:I mean, when us humans go to hostile worlds we don't jump out naked, gasp, and die. We don our impervo-force-field-belts or our stealth armor exoskeleton.
Neither did the aliens jump out and die.

Some were killed; the fleet survived. But there are plenty of examples where despite humanity's great technology our own natures - read greed/avarice - compromise us. For instance,
Dune. Spice was desperately needed despite the huge cost in mining it. Humans entered into an environment without taking the necessary precautions, and really kept making mistakes. Lives were lost to the desert and the sandworms so they could mine spice or hold Arrakis. Why is it a plot hole for aliens in
Signs to make a mistake despite their technology? Can't simple greed or desperation betray them?