Visible crew/equipment: When the Scoobies are attempting to leave Buffy's house by using magic, we see a close up shot of the house's front door knob. None of the Scoobies are reflected in the door knob even though they're standing right in front of it. There is also a fairly large black object reflected in it. A film crew perhaps?
Other mistake: As Spike follows Buffy into the hallway by her front door we see Spike's reflection in the mirror. Vampires do not have reflections, so Spike should not have been visible.
Continuity mistake: The wreath on the front door of the Summer's house disappears just after Tara tells Willow she will be doing the spell. It reappears in the next shot from outside the house.
Continuity mistake: The security tag on Buffy's new jacket shifts when Buffy first sees it. (00:12:50)
Chosen answer: Angel is saying that he is still jealous and Buffy recognizes that this is his way of saying he wishes that they could be together. That is why they both smile.