About 14 minutes into the episode, David is walking Kelly, Donna and Steve through his Grandparent's house. Just as they walk past the stairs, a member of the filming crew can easily be seen in the mirror in the middle of the room.
Brenda lost her wallet, but is able to call home from a pay phone. She couldn't call collect because her parents thought she was staying at a house with her female friends and calling collect would give away the lie.