Wrestling with Demons - S3-E12
Deliberate mistake: When Piper froze the demons (near the wrestling) one of the demons moved when she froze him.
Continuity mistake: When Piper and Prue are standing in the bedroom with Charlotte, Prue's hand moves from covering her mouth in one shot, to being by her side in the next.
Sight Unseen - S3-E5
Factual error: When developing a photo it's first put into a developer chemical, which shows the picture up, then a stop, which stops it from developing anymore, then a fix which "sets" the photo. But in the basement, Prue puts the exposed photo into a tray with chemicals in it where it starts to develop, then into a second tray where it develops fully.
Continuity mistake: When Phoebe and Prue look in the Book of Shadows for the spell to summon Belthazor, it is written with the same artistic calligraphy as the rest of the Book. But this spell was written by the sisters themselves in episode 3-8: "Sleuthing With the Enemy." As a result, it should have a handwritten appearance similar to the pages Phoebe was working on at the beginning of this episode.
Wrestling with Demons - S3-E12
Continuity mistake: When Rasputin first lay on the couch, he was at the end of it, but two shots later he was suddenly in the middle of the couch.
Pre-Witched - S3-E17
Other mistake: During a flash back of Grams in the kitchen she puts a rose in a pot, then Piper walks in, they talk and Piper starts to add some salt and a couple other ingredients into the pot. Grams asks how she knows what to add, Piper says says something about mustard - Piper wouldn't know what's in it already, she just walked in. And she never even finds it strange that there's a rose with a stem in it.
Sight Unseen - S3-E5
Continuity mistake: Cole goes to the manor, turns the AC on, knocks a lamp on the ground and opens a window, then shimmers up to the attic. When the sisters come home all the windows are open, but Cole opened only one downstairs.
Continuity mistake: When Phoebe adds the photos to the Book of Shadows, Phoebe writes "Cole's human form" with large letters, then in the shot facing Phoebe as she says, "Your date, the guy you've been smooching," we see it's underlined with smaller writing, but in following shots it's back to the original larger lettering without the underline.
All Hell Breaks Loose - S3-E22
Visible crew/equipment: During the scene in the kitchen, after Piper reads through all the faxed interview requests, in the wideshots facing Darryl the reflection of the moving boom mic is visible on the glass at the top, center of the screen. (00:21:15)
The Demon Who Came In from the Cold - S3-E19
Visible crew/equipment: After Prue removes the piece of Belthazor flesh from the freezer it cuts to Cole finding Phoebe's note in his pocket with a closeup of Cole, and at the start of the next shot the reflection of the boom operator holding up the boom pole and mic can be seen on the glass window, behind Pirelli/Vornac. (00:28:05)
Visible crew/equipment: After Lukas kills the other demon so he can move forward with his plan to go after the witches, when it cuts to the manor's foyer as Prue and Phoebe walk in, the green T-mark is visible on the rug at the bottom of the screen. (00:08:15)
Visible crew/equipment: After the Grimlocks enter the manor Leo calls for Piper then rushes out of the kitchen, and when it cuts to the shot of the dining room the edge of the crew's black mat is visible at the bottom of the screen. The black mat is again when the sisters are pulled into the time portal, though the only thing we should be seeing is the fringed area rug. (00:04:00)
Continuity mistake: While Dantalian tries to steal the Book of Shadows from the attic Piper and Phoebe surprise her, then when Phoebe kicks Dantalian and she falls we see the stuntwoman's footwear has chunky sole ridges, but when the sisters approach Dantalian her shoes have heels. (00:32:10)
Blinded by the Whitelighter - S3-E11
Visible crew/equipment: After the opening credits, when it cuts to Piper and Leo in the dining room the green tape mark is visible under the table, and the red T-mark and long blue tape mark are also visible on the crew's black floor mat behind Leo. (00:04:45)
We All Scream for Ice Cream - S3-E10
Visible crew/equipment: When Phoebe gets an IM on the laptop Prue walks over to her, and just as Prue sits down at the table we can see the blue tape mark on the floor, where she had been standing. (00:05:50)
Visible crew/equipment: After following the signs that lead to the demolition site, when Prue unlocks the chain on the door and enters the loft, the T-mark is visible on the floor at her feet. (00:03:45)
Visible crew/equipment: After Phoebe tells the others that Emilio will be getting arraigned at night court in an hour, when it cuts to Leo and the sisters walking in the court hall, the shadow of the boom mic is moving at the top, left side of the screen. (00:33:45)
Revealing mistake: The sound of Phoebe writing with a permanent marker was added in, as you can see that the marker never touches the paper. Then after a few seconds Phoebe stops writing to listen to Prue and her marker isn't moving but the sound of writing can be heard. (00:05:30)
Pre-Witched - S3-E17
Revealing mistake: At the beginning of the episode Piper and Leo are in the shower together - at the bottom of the screen you can see Piper has on a flesh colored towel.
Answer: "Hush, Hush, Hush" Paula Cole.