Chick Flick - S2-E18
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: Phoebe had to touch both Jane and Malcolm for them to be trapped in the painting, so how come she didn't have to touch Piper and Prue for them to all be freed? (00:39:25)
Continuity mistake: Just after Olivia has killed Mr. Montana and everyone goes running up to see what has happened, Phoebe waves to Paige through the window of the Calloway's house which is shown to be right next door to the Montana's house. Earlier in the episode it had been established that they lived across the street.
The Power of Three Blondes - S6-E4
Continuity mistake: When the Stilman sisters are talking about who gets which powers, Margo(the youngest)had her hand by her side, but in the next shot when she talks about Mitzy's (the middle sister) attitude, she has her hand on her shoulder.
Continuity mistake: If Leo can't hear the girls call him when HE is underground, he shouldn't be able to hear the girl's call him when THEY are underground and he doesn't know they are at P3 until a few minutes later.
Continuity mistake: Piper says she wants to go to Paris by plane not by orbing, but in the episode "From Fear to Eternity" flying was Piper's greatest fear.
Be Careful What You Witch For - S2-E22
Continuity mistake: At the end of the episode, when Prue shuts the door magically it shows the inside of the house. There should be a doorway parallel to the front door that leads from the foyer into the dining room, but instead there is a wall.
Continuity mistake: After Phoebe tells Piper about the balloon plan, when Piper starts talking about Leo she fills the blender on the counter, and in the two shots facing Piper the white lid is on top of the blender, but in the shot facing Phoebe the lid is gone before she turns it on. (00:19:10)
Continuity mistake: When Piper writes the name "Nell" backwards on the castle window she uses two fingers so each letter is doubled lined, but when the name is viewed from the outside all the letters are single lined. Additionally, after she writes the backwards "N" on the bottom right window, in the next closeup of the swords' pointy ends that window is blank. (00:30:20)
All Hell Breaks Loose - S3-E22
Continuity mistake: When they first bring the doctor to the manor the sisters tell him they're not sure who's trying to kill him, then a few minutes later Prue tells him exactly whose trying to kill him, Shax, the Source's assassin.
Continuity mistake: In the shot where Leo gets his wings back, his eyes are brown, usually they are blue.
Continuity mistake: In this episode, an invitation to Piper is addressed to 1329 Prescott Street. But in episode 1-7: "The Fourth Sister," the Halliwell sisters put up a flyer for their lost cat, and it gives their address as 7571 Prescott Street.
Continuity mistake: In the scene where Phoebe dangles the slumlord from the roof, the TransAmerica Pyramid can be seen behind Phoebe and Cole. A subsequent shot, after Phoebe tosses the slumlord back onto the roof, is take from the opposite side, but the TransAmerica Pyramid is still behind them, and is much closer. (00:25:25)
The Courtship of Wyatt's Father - S6-E16
Continuity mistake: When Gideon warns Sara not to use magic to put the books in the library back on the shelves, her arms are at her sides. A second later, the shot changes to over her shoulder as Leo orbs in and she has a nearly full armload of books. (00:08:55)
Continuity mistake: When Leo and Ramus are talking in front of the bay windows, the door behind Ramus switches from closed in the wide shots to open in the close-ups. (00:31:50 - 00:33:00)
Chick Flick - S2-E18
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. (00:22:15)
Something Wicca This Way Goes - S7-E22
Continuity mistake: Phoebe's shoes change between shots. Near the end, while fighting Zankou in the basement, he hurls the sisters to the ground and Phoebe is shown wearing sandals. When she stands up, she is now wearing sneakers.
Siren Song - S5-E4
Continuity mistake: When Piper and Paige fall out the window and land in the dumpster, in the wide shot the garbage bags are white, and in the close-up they're blue. (00:16:45)
Continuity mistake: At the beginning of the show when Piper comes into the kitchen to help Paige, she is wearing slippers. In the next shot, when she is by Wyatt's chair, she is wearing flip flops.
Continuity mistake: When Cole gives Phoebe his card on the school campus, it disappears and reappears between shots. (00:23:25)
Answer: That was a mistake in the series.
Also, the episode is called 'Babies First Demon' and this alone tells us that it's Wyatt's first time in the field (so to speak) and as the sisters say, they've done a good job of clearing up their own magical messes so far. Nobody really knows how advanced Wyatt's powers are, or will become. That's why the cleaners appear, to nip things in the bud. The Cleaners didn't want to chance that the sisters could clean Wyatt's magic up, just incase they couldn't. Therefore intervening themselves, just in case.