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.

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.

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

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.

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.

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.

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.

Revealing: When Darla is spying on Buffy and Willow in the library, her reflection is seen on the side of the bookshelf.

Plot hole: In "I Robot, You Jane", how exactly does Willow scan Moloch out of his book when the scan is only about two thirds the width of it?

Continuity: Buffy's birthdate starts at 1979. In "I Robot, You Jane", when the demon pulls up Buffy's file in the school system, it shows her year of birth as 1979 and that she is a senior. But when her file comes up on the student's computer screen, its changed to 1980 and sophomore. It wasn't until towards the end of season 1 in "Nightmares" that her birth year is 1981 (on her tombstone before she comes out as a vampire.)

Revealing: The Master's artificial thumbnail is visibly falling off in a few shots of the opening teaser.

Continuity: In the season 1 episode "Nightmares", Buffy is talking to Willow about her mom's divorce and she shuts her locker. A few seconds later she shuts her locker again.

Visible crew/equipment: At the very end, as the invisible girl gets taken along a corridor by the FBI agents, check the top of the screen - a boom mike creeps in as the agent says his line, then is withdrawn.

Continuity: When Buffy drowns in Prophecy Girl, she falls into the pool with her hair tied in a ponytail and her arms under her. When she is discovered by Angel and Xander, her arms are by her sides and her hair is loose.

Revealing: When all the vampires are saying "for the dark", and one gets staked, there's a mark on his shirt where the stake's about to come through before it actually happens. Plus Buffy's hands are in the wrong place for her to have pushed that stake through anyway. Not only that, but the mark isn't even close to the vampire's heart to begin with.

Revealing: When Buffy sets the vampire alight, his face suddenly gets very shiny, showing the fireproof gel that was applied to the actor's skin.

Continuity: In the season two episode, 'When she was bad', in the scene where Buffy smashes the masters skeleton with a sledge-hammer she smashes the rib cage to pieces. Suddenly the rib cage has again become completely intact and she smashes it to hell again.

Continuity: While studying at the Bronze, Buffy and Willow leave their books on the table to go and dance. Spike calls them outside to fight a vampire, and when Xander runs back inside to grab a stake the books have all been put back into Buffy's bag.

Continuity: When Cordelia comes up to Buffy talking about how "even slaves get minimum wage", in pretty much every shot her arms switch from being at her sides to crossed in front of her, held behind her or on her hips.