Character mistake: The banner of the fundraiser event for the Gotham upper class says "Childrens Hospital", no apostrophe. (00:11:55)
Character mistake: At the meeting in Washington the general says nothing more frightening than a soldier with his M16A1, but they were using M16A2s.
Character mistake: When Walter brings Cynthia's dog in the carrier to the bowling alley he refers to it as a Pomeranian while it is actually a terrier. Somewhat related, when the the Nihilists confront Dude in the bathtub, the dude refers to the ferret as a marmot. Walter later refers to the ferret as an amphibious rodent. Perhaps he was thinking of a mink.
Suggested correction: These were purposeful taxonomic (funny!) jokes.
Character mistake: The complaint that Robert Duvall is reading has a very obvious typographical error describing the decedents' conscious pain and suffering, 'concously'.
Character mistake: Sheridan (as Roberts) takes a job as a tow truck driver while laying low from the U.N. killings. He claims he had the gun for protection, but he must have realised if he ever had to use that weapon on the job his prints would have been run anyway, so why on earth would he take any kind of job that requires him to need a weapon if he's trying to lay low?