Visible crew/equipment: In the scene at Buffy's house, her mum comes into her room and says "Buffy, I'm home". As she says this a boom mic is visible above her head.
Revelations - S3-E7
Visible crew/equipment: In the Buffy/Faith fight right around when Buffy says "We can work this out..." You can see what appears to be a boom mike bob in and out of the frame in top left. (00:36:15)
Visible crew/equipment: Near the start, just after Buffy kicks the vampire onto the roundabout, check the top left corner of the screen as she says her line - boom in shot. (00:02:35)
Visible crew/equipment: Just after Cordelia says "let's go to the Bronze", check the top of the screen - a microphone drops into shot for Harmony's line "is that a joke?" (00:16:20)
Visible crew/equipment: In the scene where Buffy is packing Joyce's clothes into a suitcase you can see a mic moving at the top of the shot as they walk through the door.
Visible crew/equipment: There's a boom mic visible when Cordelia is talking to Harmony and the other Cordettes. It's the first scene in the alternate universe and they're standing inside a classroom of Sunnydale High (Cordy says something about going to the Bronze).
Visible crew/equipment: Near the end after freeing the prisoners, Buffy fends off Ken's henchmen on a raised platform. At some point during the fight she is grabbed by one of the henchmen and punched in the stomach by two others. She then breaks free and throws one of them off the raised platform - onto a large crash mat. Please note that this is a separate mistake to the one already submitted as it is talking about a different crash mat.
Visible crew/equipment: When Buffy is going through the murdered Professor's office, Angel seems to trip through the doorway. To the top right above Angel's head a boom mike is visible twice.
Homecoming - S3-E5
Visible crew/equipment: When Buffy and Faith are in the library, a person's arm wearing a white shirt can be seen on the left side of the screen behind Buffy in one shot.
Visible crew/equipment: While Buffy, Giles, and the gang are in the library fighting the demon that came out of the Hellmouth, the camera zooms toward the door that leads into the hall, where you can see Xander being chased by the dead guys. As the camera zooms in closer towards the round window in the door, you can see its reflection in the glass when the strobe light flashes. (00:36:10)
Chosen answer: He had larangitis and because of the shooting specifications they had to have him shoot the scene with a bad throat, they then re-recorded his lines and dubbed them. At various points during the scene and indeed the episode you can see him touch his throat or rub it.