When Caroline is telling Stefan about Matt, Stefan tells her to compel him and asks if the vervaine is out of his system. Caroline says she slips it in his soda but didn't get to the night before so it should be out of his system. All other times it takes three days for the vervaine to leave someone's system.
When Stefan and Damon arrive at Isobel's house ("the nicest foreclosure in town"), they walk inside into the front hall and pause to decide where to go next. In a long shot we see the front door suddenly swing inwards by itself and stop just short of closing. This happens at least 30 seconds after the brothers have passed through it, the position of the door means it could not have been a gust of wind, the timing means it could not have been a normal spring hinge action, and the Salvatores are shown at least 2 feet away from it when it starts to move. In addition: in the very next shot when Damon walks past the door, it is back to being half open, and the shot after that the brothers walk out and Stefan slams the (now completely open) door shut.