Continuity mistake: 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 mistake: At the beginning of the episode, Buffy is running from the large saws and jumps out the door, she sits up and you can see the book is fully intact and in one piece. After the opening credits Tara picks up the same book and it falls apart from being cut in half.
Continuity mistake: After Spike finishes reading his poem to his mother, the piece of paper that it's written on disappears from his hands between shots. We never hear or see him put it in his pocket and he doesn't move to put it down on the table beside him.