Previously, when Spike attacked the school, the library door was barricaded from the inside successfully, but here, the door is shown to open from the outside. Also, when Jenny leaves the library to go after Xander, the door swings outward and inward indicating that the door goes both ways.
When Cordelia and Xander leave the school it's daytime, but on the next shot when they walk towards Buffy's home, it's already dark.
As Xander is doing his slow motion walk down the hallway, just as he passes through the doors we see a black guy and white guy behind him wearing a similarly coloured button down shirt. After the camera cuts back to Xander twice, we see them again, this time standing at the other end of the hall on the right-hand side.
Diana was not considered the goddess of love, as Amy calls her.
After Buffy has been turned into a rat and she runs away, the rat is clearly male. Later, when rat Buffy encounters the cat, the rat is female.
When Willow tries attacking Xander with an ax, causing a scramble for the it, the ax gets waved around in the air, and then its shaft bends a bit, indicating that it's possibly made of rubber.
Amy and Giles are in the chemistry lab performing a spell reversal. When the potion lights up with a blast, Giles' tie flies back and a string is visible.
Two times, Xander blocks a doorway with heavy/bulky items. But in both cases, the doors open outwards, rendering his blockades useless.
At 38:05, Joyce swings a knife at Xander and Cordelia. It makes a slicing sound despite not making contact with anything.
When Angelus throws Xander off the roof of Buffy's house, you can see a row of six two-by-fours propping up the porch rafters to support the weight of the stunt men on the roof.