Deliberate "mistake": While it is established that Angel doesn't age, it's obvious across both Buffy and Angel that David Boreanaz gets older. More unavoidable than deliberate, but still worth noting.

Continuity: When Giles is giving his speech about the Hellmouth the books Buffy's holding keep changing from facing him to facing Buffy and back again.

Audio problem: When everyone is in the Bronze - just before the vamps show up - you hear the first line of a song being played, Ballad For Dead Friends by Dashboard Prophets, cut to outside and you see the vamps strolling along and killing the doorman, then cut back into the Bronze and the same line plays again. This is a total error in cutting the show, it is stated there is no live band but still the same line plays twice when that is not how the song goes.

Audio problem: When Buffy kills the vampires dragging Xander at the beginning, we hear two impact sounds but don't hear either of them turn to dust. They were only a few feet away and there was no other sound to cover it up.

Plot hole: When Buffy visits the crypt that leads to the Master's lair, Angel is waiting for her in the shadows. How did he get there in the middle of the day? Other episodes clearly show that he waits until it's dark to go out, even with imminent danger threatening the Scoobies.

Continuity: Willow fills the test tube halfway with the witch-detecting potion, but when she hands it to Buffy it is only one-quarter full.

Revealing: The edges of Cordelia's solid white contacts can be seen after she is blinded.

Continuity: At home Buffy helps her mother open a crate. She tears off the cover and leaves it hanging by the side. Next shot the lid is back on. Not nailed anymore of course, but there was no time to put it back on.

Continuity: When Cordelia gets out of the car, she shuts the door, but in the next shot the door is open and is then hit by the truck.

Continuity: When Xander and Willow are talking in the hall about his invisibility, the pen Willow toys with changes position back and forth between front and reverse shots.

Continuity: At the beginning Buffy asks Giles, "You'll be stopping me how?" and he is facing her. Cut to him and he's looking down and away.

Continuity: In the episode 'Teacher's Pet', when Ms. French is eating her bug sandwich, her sleeves go from being up in the long shots to being pulled down in the close-up of the sandwich.

Factual error: In Teacher's Pet, Doctor Gregory was giving the class a lecture about ants. But he projects an image of a beetle onto the wall behind him.

Continuity: When Buffy finds Dr. Gregory's glasses on the lab floor she places them on the table, from the long shot she places them at the left end of the table near a plastic tub with a white lid, with the glasses open. Then it cuts to a close up where they are in front of a book on the right side of the table and are closed. Then cut back to the long shot and they are in the original place.

Factual error: In the famous scene where Buffy tells Giles, "If the Apocalypse comes, beep me," she grabs her pager from out of shot. Trouble is, she's standing in the middle of her hall and there's nowhere she could have picked the gadget up from.

Continuity: When Buffy is talking to Owen at the end, there is a woman wearing a red/black checkered jacket, sometimes carrying a red bag, walking up the stairs behind Owen several times. You can also see her behind Buffy in shots facing her.

Continuity: In "the pack" nearly all the supposed video clips of hyenas Willow watches on her computer monitor throughout the episode are actually of African wild dogs.

Continuity: 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: Vampires can't enter a house unless invited. Throughout Buffy this appears to be some kind of force field, as if the vampire has run into a brick wall. But in this episode, the vampire chasing Buffy and Angel gets its arm through Buffy's front door.

Continuity: In the episode 'Angel', during the climax at the Bronze Buffy puts down her crossbow and walks towards Angel, about 5 steps. When Darla bursts in a few seconds later the crossbow is back at her feet.