Continuity mistake: The first night that the Gentlemen float through the college, they are on the 2nd floor one minute (all the room numbers start with 2), then they turn a corner and are suddenly outside room 118, a floor below.
The Harsh Light Of Day - S4-E3
Continuity mistake: When Buffy and Spike are fighting on campus during the day, Xander tries to help Buffy but Spike throws him against a lamppost. When he lands in the ground he falls completely on the grass on his side but if you look behind Spike in the next shot he lies half on and half on the grass on his front.
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: When Tara is being chased by the monster and she falls, she says a spell and white smoke comes out of her hands but it is coming out of the sleeves of her shirt, the way she holds her hands up suggests this as well.
Continuity mistake: When Oz turns back into a werewolf, he chases after Tera. She hits him with a chair and he falls to the ground and passes out. We then see The Initiative show up and learn that Riley has shot Oz with a dart (it's sticking out of Oz's side). But two shots earlier the dart wasn't there.
Visible crew/equipment: At the end when the gang leave the high school, stage lights are reflected in the broken glass of the double doors that they exit through.
Continuity mistake: When Oz shows up at Buffy and Willow's dormitory, Willow has a lump or a pimple above the left corner of her mouth. It disappears later in the episode when she's talking to Buffy about her feelings for Tara and it returns at the end when she and Oz are in his van.
Revealing mistake: In Xander's dream, when he climbs into the back of the ice cream van, for a split second before the window goes out of view the backdrop cuts out and the blue screen is visible. Only visible in widescreen version.
Revealing mistake: When Jonathan assists Buffy at the beginning of the episode, he enters through the glass ceiling of the mausoleum, which shatters into squares. Although the audio is the sound of glass shattering, the pieces of "glass" flutter down, revealing that the squares are paper - simply for the safety of the actor during the stunt. (00:05:00)
Continuity mistake: The first shot of Maggie Walsh being impaled from behind with the skewer indicates that there is no one standing close by, judging by the amount of negative space around her. However, following shots reveal that the skewer is coming straight out of Adam's wrist, therefore he should have been visible in the previous shot.
The Harsh Light Of Day - S4-E3
Continuity mistake: Right before Spike jabs Buffy in the face on the college's campus, there are a ton of people around. But after he jabs her in the face and they start fighting, all of the people are gone.
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.
Plot hole: Willow hacks into The Initiative's computer system and discovers air ducts and electrical conduits leading to Adam behind 314, but the room doesn't show up on the schematic. It seems unlikely that nobody who didn't know about Adam would have noticed this and investigated.
Revealing mistake: When the Gentlemen are chasing Tara in Stevenson Hall, in the first hallway two Gentlemen are floating down the corridor and you can tell they're on wires because the one on the screen's left "jumps" a little as if his wires got snagged.
Other mistake: In the scene where Spike escapes from a blind Giles, he pushes Giles out of the way and does not get a shock to the head from the chip in his head, which normally goes off with the most minor hint of violence.
Continuity mistake: When you first see Adam lying on the bed, before he wakes up you see his human side of his face on his right side. In the next scene the camera is over Maggie Walsh's shoulder and the human side of his face is now on the left side. Then just after he stabs Maggie it switches back again.
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.