Continuity mistake: When the ani-men break into the manor the entire large center glass of the left door ends up broken, but later while Phoebe is looking for the hydrogen peroxide, Prue notices the front doors and the left door's center glass is intact with only the bottom corner broken. (00:22:00 - 00:27:05)
Continuity mistake: After the manor is broken into, in the following shots while everyone is in the foyer the left front door is wide open in most shots, but in some other shots both front doors are closed during this scene. (00:21:50)
Continuity mistake: After class, when Phoebe is talking to her study group she pulls out the flyer for P3, and in the first shot the flyer is in Phoebe's right hand, but in the next shot she's holding it out in her left hand. (00:01:40)
Visible crew/equipment: While Phoebe is telling Prue about the abandoned baby, Piper comments that the baby is like a car alarm, and as the sisters walk into the foyer the white T-mark is visible on the rug in the foyer. (00:07:20)
Visible crew/equipment: After the shots of the kids arriving on the first day of camp, when it cuts to Prue and Phoebe in the car, we can see the reflections of the camera operator and camera dolly on the surface of the car. (00:22:35)
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 Leo comes to the manor to tell Piper about Masselin, during the conversation Prue is not wearing her choker in the shots facing her (with her arms crossed) and Phoebe, but in the next shot when Leo tells Piper that he knows she's upset we see Prue's choker suddenly around her neck. (00:11:50)
Visible crew/equipment: After Prue gets off the phone with Barker and tells Phoebe about it, when Piper runs into the kitchen with the news about Dishwalla, the reflection of the moving boom pole can be seen on the glass cabinet. (00:10:00)
Visible crew/equipment: While Phoebe begins her "fifteen minutes of channel surfing" she has the burning premonition and cries out, then in the next shot as Prue and Piper rush in, we can see the reflection of the boom mic/pole in the wall mirror. (00:02:10)
Witch Trial - S2-E1
Visible crew/equipment: While the Book of Shadows flips its pages the sisters enter the attic, and after Piper asks how the book does that, in the next shot the feet of a crewmember can be seen moving quickly out of shot, at the bottom left side of the screen. (00:03:15)
Chick Flick - S2-E18
Character mistake: After the horror movie characters were killed in the attic, the sisters hear the door bell ringing. When they get to the bottom of the stairs and start walking towards the front door, you can see the actor playing Billy smiling even though they're all supposed to be on edge.
Factual error: Phoebe is going to be burned at the stake for witchcraft like they're starting the Salem witch trials again, but witches weren't burned, they were hanged.
Continuity mistake: When Prue leaves Buckland's, she's wearing a red tank top, but when she arrives at Camp Skylark, her shirt is different, both in style and color. She can't have stopped to change, because it's mentioned she left the auction house and headed directly to the camp. (00:07:00 - 00:09:20)
Continuity mistake: When Prue is sitting at home bored, she spots the vase with the flowers. In one shot the vase is on the left, and in the next shot it's on the right, then Prue moves it to the left.
Continuity mistake: As soon as the water demon enters Sam, we can see that Prue's hair is completely dry. Then when she flips the switch to electrocute Sam to kill the water demon, her hair goes from dry to wet without ever coming into contact with any water. (00:36:25)
Be Careful What You Witch For - S2-E22
Other mistake: Phoebe says to the genie "you've been stuck in the bottle for 200 years?" Later the genie says he will be an unwelcome house guest and not put the CD's back in their case. If he was in the bottle for 200 years how would he know of CD's?
Continuity mistake: When Prue, Piper, and Phoebe return from the future, Prue and Piper hug Phoebe in relief. In the following shot, Piper wraps her arm around Phoebe again. (00:39:20)
Factual error: During the ritual, we can see that the snake that is magically transformed into a man is a milk snake. But it's not poisonous, it's a colubrid. The creators apparently wanted to use its resemblance to a poisonous coral snake, which is an elapid. (00:02:35)
Continuity mistake: Near the end of the episode Piper is talking to her sisters in the parlor with her watch is on her left wrist and a bracelet on her right wrist. She goes upstairs to her room to cry and her bracelet and watch have switched places. (00:39:05 - 00:40:00)
Continuity mistake: When Phoebe first meets and talks to Nathan in the hospital, she has no ring on her right hand in shots showing her face, but in any shots from behind her she has a ring on. The ring appears and disappears between transitions during their conversation. (00:07:50)
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.