Continuity mistake: In the teaser, Phoebe took off her messenger bag while she was sitting in the chair talking to Prue, and she left it there when she went up to get the door. For the rest of the scene at the house, including when Phoebe and Prue ran out of the door, Phoebe was not wearing the bag. Then, when we saw them outside immediately thereafter, Phoebe was wearing the bag again.
Continuity mistake: After Phoebe kisses Billy, she sees that the makeup over his lips has washed off and that they're in black and white again. While she applies more to him, the phone rings, Billy turns his head, and his lips are normal. In the next shot, they're back to being in black and white.