After Spike pulls out the crossbow and shoots the vampire, he pulls the string back in the wide shot and then again when it switches to the close-up shot.
When the vampire Buffy is fighting kicks the window on the car door, it shatters before his foot hits it.
The lady/ladies who do Buffy's stunt work are always very visible, as in you can easily tell when it's Geller or when it's another lady instead of her.
When Buffy was talking to Xander, she said she had been gone (dead) for 3months but in Bargaining: Part 2 (2001), Spike tells her that she'd been gone for 147days and would have been 148 but that day doesn't count (since she was alive again). Obviously the math doesn't add up....3 months would only have been 90days. 147 is roughly a little under 5 months.
Although Halloween is supposedly the night vampires take a break from feeding on humans, Giles says: "Mist. Cemetery. Halloween. This should end well."
When Buffy and Xander go out on the front porch for air, you can see the boom microphone reflected in the front windows of the house.
Buffy says she was only out for 3 months. In "After Life" Spike told her she was out for 147 days, 148 if you include the day he said it. That's nearly 5 months.