Continuity mistake: During the party, Natasha has just walked away after flirting with Banner. On the bar behind him is a glass of red cocktail next to a silver cocktail shaker. In all subsequent shots while Captain America is talking to Banner, the two have moved much closer together. (00:27:00)
Continuity mistake: When Scarlet Witch enters the fight, after Hawkeye's pep talk, there's a payphone booth to her right, several feet away. In shots of her fighting, the double doors are seen behind her. When Hawkeye nods at her, in the next shot of her, she is standing with the phone booth behind her. And then she's not near the phone booth when Hawkeye and Scarlet Witch start to leave.