Continuity mistake: When Willow hides under the table in the classroom after fleeing The Pack, we see that it is on legs and doesn't touch the floor. Yet when Xander comes in and scans the room, he sees the table but Willow's feet aren't visible, even though they should be judging by the height of the table from the floor.
Continuity mistake: When Willow is unsuccessfully trying to tutor Xander outside towards the beginning of the episode, after Willow warns Xander he might flunk math, he reaches up and massages his face with his hand. When he does this, he has a pen in his hand. When the camera cuts to the opposite angle, the pen vanishes. Then, when the scene cuts to a wideshot about 10 seconds later, suddenly his hand is in a completely different position between cuts.
Continuity mistake: When the zookeeper catches Buffy and Willow trying to sneak into the hyena exhibit in the beginning, when Buffy and Willow turn around, they get close to each other but there's still at least 6-8 inches of space between them. When the camera cuts, though, they are suddenly pressed literally right up against each other, to the point they are borderline huddling.
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.