When Giles injects Buffy with the needle, her shirt sleeve goes from being up, to, when he 'wakes' her up, being down without anyone pulling it down.
At the end when everyone is in Buffy's kitchen making PB & J sandwiches, Buffy is putting jelly on the piece of bread all the way to her right. When she picks up the peanut butter, the jelly is in one big glob on the bread. Then the camera switches to Oz and then back to Buffy, but the jelly is now spread out. The camera changes to Xander and then back to Buffy and the jelly is now a glob again, but is much more messy than the first glob.
Time stated by Giles is significantly different to time shown on clock.
At 18:05 when Buffy is opening the gift that Angel gives her for her birthday you can see the bulky square mic pac on Sarah Michelle Gellar. It's clipped to the back of her pants and is under her cardigan.
When Buffy fights the vampire at the beginning of the episode, the boom mic drops downs into view.
The audience is told several times throughout the series that vampires do not show up in photographs, but Zachary Kralik is seen in a photo that he took of himself and Joyce.
Krelik would have needed to rob several stores or a warehouse to obtain that much Polaroid film. It was becoming obsolete at the time because of the advent of digital cameras.
Usually it takes a day for a victim that has been turned into a vampire to "wake up", but this time it is just a couple of hours.
At roughly 6 and a half minutes in, Willow tells Buffy that 18 is an important birthday because she can now vote and be drafted. Buffy can't actually be drafted, though, because women in the United States cannot be drafted. Only men can be drafted.