2. The Microwave Emitter (Batman Begins)
One of the most frequently cited problems with Batman Begins is the plot hole surrounding the Microwave Emitter device that Ra's Al Ghul intends to use to evaporate Gotham's water supply and cause the Scarecrow's nerve gas to be freely dispersed throughout the city as an inhalant. However, this plan overlooks one basic fact of human physiology, that the vast majority of the human body is water, and so setting off the Microwave Emitter in Gotham would in effect cause everyone to die instantly, rendering the device - which was intended to turn everyone crazy and therefore raze Gotham - totally pointless. It's one of those annoying plot holes that once you realise it, it's impossible to watch the film the same way again; it just seems like such a silly oversight for such a talented, cerebral filmmaker. Maybe Nolan just didn't care and wanted us to gloss over the science in favour of the dramatic heft of the scene. Is it still a great movie? Of course, but there are countless other ways the toxin could have been dispersed that didn't fly so brazenly in the face of science.