Continuity mistake: When Katie is talking to Grace, she has the works of Confucius under the Bible and Koran. When Grace says she likes how people won't die any more, the shot changes and the works of Confucius is now on top.
Continuity mistake: In the beginning, after the attack, when the guy is shot in the head, his left arm is crossed over his body (and stays that way after being shot). When the camera angle changes, his left arm is now lying flat on the ground.
When Will tackles Andrew, his shirt is lifted up exposing a blue undershirt that's tucked in, which is also behind his gun. There's two shots of this, but in the next shot, right before Will punches Andrew, we don't see the undershirt.