At 23:15, as Spike stands up, his reflection can be seen in the mirror to the left of the door in the background, visible past Giles' right shoulder. Also, from 24:27 to 27:07 his reflection is visible numerous times in the glass front of the bookcase next to his chair.
When Buffy finds Spike standing out on the lawn, the mast of the mobile lighting tower can be seen against the dark sky in the upper right portion of the picture.
During the fight in the crypt, Spike is attacked by a demon. Expecting pain or not, he would defend himself and thus find out at this occasion already that he can still hurt demons without being reined in by the Initiative's behavior modification chip.
When Amy is briefly turned back into a human, she is sporting a full face of make-up and shiny red lipstick. She was not wearing this make-up when we last seen her, in Season 3's "Gingerbread". There is no plausible explanation as to why she would have this make-up on.