When Buffy and Willow group-hug Xander, one camera angle shows Willow's right arm outside Buffy's left, while the opposite angle shows it inside, so as the view cuts back and forth, so does Willow's arm.
When Anya is comforting Xander about the Scoobies' fight the previous night, Anya's arm changes position from Xander's nipple line in the close up shots, to his collar bone in the overhead shots.
When Buffy pulls the power battery/heart out of Adam's chest, the way she is holding it changes between shots. In a close-up, she is holding it in her open palm, horizontally. Then in a far shot, she is holding it up and down, vertically. Then in the final close up, she is holding it in her open palm again, horizontally.
Buffy says about Adam, "According to Riley, his power source is uranium core embedded somewhere inside his chest." In fact, it was Jonathan who provided that information.
Sarah Michelle Gellar had obviously lost weight between the 3rd and 4th seasons, therefore the difference between her and her stunt double is much more noticeable during the fight sequence with Adam.
In the fighting scene between Forrest and Riley, Riley gets thrown over a table. In the next shot, you can see the chest-belt under his shirt (the thing with a wire to pull him back in the next shot).
On an outside view of Lowell House, a piece of camera is visible in the upper left corner.