Continuity mistake: In the scene where Silk Spectre II visits Nite Owl II at his home, the small mole on her cheek disappears only to reappear again when they leave to visit Hollis Mason (Nite Owl I). It doesn't appear to be a staple of Spectre's makeup in any way and is instead permanent, as it was present when she left Dr. Manhattan to visit Nite Owl (directly before) and on the way to visit Hollis (directly after) as well as through the rest of the film.
Trivia: This is for the trailer rather than for the final film, but worth a look. At 1:33 in the trailer, just after seeing Rorschach slam someone against a wall, we see another fight. Pause it and look at the guy in black - he's holding a walkie-talkie, which in the next shot becomes a gun. This is only trivia, not a mistake, because it's only valid for the trailer. The MPAA don't allow guns to be pointed at the screen in trailers, so Zack Snyder, in a tribute to the infamous gun-editing from E.T., replaced the gun in that one shot with a walkie-talkie.
Rorschach: You forgot how we do things, Daniel. You've gotten too soft. Too trusting. Especially with women.
Dan Dreiberg: No, listen, I am through with that! God, who do you think you are, Rorschach? You live off people by insulting them and nobody complains because they think you're a damn lunatic! I'm sorry. I shouldn't have said that, man.
Rorschach: Daniel? You are a good friend.
Question: Why did Adrian Veidt also have to infect Moloch with cancer? The comedian mentions to Moloch that Moloch's name was on a list together with Janey Slater's (and others?), who were presumably the ones Veidt infected with cancer. So why Moloch, too? In order to make Dr. Manhattan and the world think that Dr. Manhattan was causing cancer? He had already infected Janey Slater and Wally Weaver who had more contact with Dr. Manhattan. I would think, Moloch and Dr. Manhattan only had brief contact with each other when Moloch was captured.
Question: I don't quite understand why Dr. Manhattan had to kill Rorschach. That is, I don't quite get why that was the only solution. Rorschach was a valuable member of the Watchmen, and in the type of world they were in (chaos, corruption, murder, etc) one would think that they would want to keep as many of themselves banded together as possible. Couldn't some sort of negotiation or compromise have been reached/agreed to by Rorschach instead of him being killed?