Continuity mistake: When Oz leaves and holds Willow close to him, the position of their noses changes depending on the camera angle. In the shots of OZ they're pressed together and in the shots of Willow they're not.
Continuity mistake: When we see Veruca eating at the table, she reaches for a cup as we see Oz coming up behind her. The shot changes and we see her turning around and reaching for the same cup again, though she never had time to put it down.
Visible crew/equipment: In the scene where Willow visits Xander to discuss what may be going on with Oz; towards the end of the scene, when the camera is on Willow, you can see the sound mike at the top left of the screen next to the green crate in two different shots.
Revealing mistake: Towards the end when Oz says to Veruca, "You don't wanna find out what I am", and partially turns into a Werewolf. You can tell that both of the actors were filmed separately for the CGI's sake as Oz stands out from the picture more than Veruca does. The same effect is obvious during "Doppelgangland" in season 3 where there are 2 Willows onscreen at once.
Revealing mistake: In the scene when Oz stops the female wolf from attacking Willow, and they both change and Oz tears her neck out, if you look closely, you can see the actor's real skin at the neck.
Revealing mistake: Several times during Spike's escape from The Initiative, his reflection can be seen in the glass. Vampires aren't supposed to have reflections. (00:13:00)
Visible crew/equipment: In the scene where Spike escapes from The Initiative a black curtain can be seen to the right of the screen after the other vampire is release from his cell. The curtain serves no purpose to the set or scene and it disappears in the next shot. (00:13:25)
Factual error: In "The Initiative," Riley is looking for Spike with a heat sensitive camera and says "we've got a cold one." If Spike was at room temperature as indicated on the sensor, he would be indistinguishable from from the air and objects in the room. (00:37:30)
Continuity mistake: In 'The Initiative', Riley, Graham and Forrest are looking in through the windows of Stevenson Hall with thermal goggles looking for Spike, they see him walking towards Willow. When we see Willow and Spike seconds later he is still sitting on the bed where he was for most of the scene. (00:37:30)
Plot hole: Spike must have had his chip implanted while he was unconcious. If so, how did he attack The Initiative scientists without any pain when he tried to escape? You could argue that they programmed him to be capable of violence within The Initiative only, but why would super smart scientists program an evil being to be able to escape at the first opportunity? Joss Whedon has acknowledged this as an oversight.
Continuity mistake: At the party where Riley is talking to Buffy by the stairs, when he first comes over there is no one in the corner on the stairs but in the next shot there are two people who disappear two shots later.
Character mistake: At Riley's party, Willow tells him that Buffy is wearing a halter top when she is in fact wearing a strappy top. Being a girl, and extremely into fashion at this stage in her life after her high school years, she should have known better.
Continuity mistake: When Xander falls through the ground, he lands with his arm on, or very near a bit of wood, but in a closer shot of him just before he gets up, the wood's disappeared and other rubble has moved around too.
Continuity mistake: When Buffy and Willow are talking about the sham of Thanksgiving Day at the groundbreaking ceremony, on one angle (the one where Buffy's face is shown) there is a strong wind blowing, moving their hair about, but in the other (when you can see Willow's face) their hair aren't moving.
Revealing mistake: One of the arrows that Spike gets hit with passes through just below his left shoulder, but there are times when you can tell that it is a fake arrow because the part of the arrow sticking out at the front moves and the part at the back does not. Look at the arrow just after Buffy turns Hus into a bear.
Visible crew/equipment: During the scene of the siege at Giles', there is a shot where an Indian guy jumps through the window and helps himself by holding on to the sill. If you look to the left side of the screen, you can see it's a moving wall and that several hands of crew members are holding it so it doesn't shake.
Continuity mistake: In the scene where Anya is undressing a sick Xander in his basement, she lifts up his shirt and says 'Help me get your trousers off.' During the following conversation, in the close-up shots his shirt is lifted far up on his chest, but in the wider shots it's covering his whole stomach.
Other mistake: Just after Giles becomes completely blind, Spike gets up to get a book off of the mantle. When he does this you can, very briefly, see James Marsters reflected in the glass doors of the bookcase that was behind him, despite Spike being a vampire. (00:27:00)
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.