Continuity mistake: When the gang are playing poker in the opening shots, the position of the chips, cards, beer bottles etc., keep changing - watch then stacks of chips by Rob. They keep changing the most noticeably.
Continuity mistake: When Karen and Jack are sucking helium from balloons in the hospital waiting room, they are using a purple balloon. The balloon disappears for a few shots, then reappears as a pink balloon.
Continuity mistake: There are two balloons, a blue and a pink one, attached to a vase of flowers in the waiting room. Between shots the pink balloon shrinks half its original size as Jack is talking about a man losing all his limbs.