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: Near the end of the episode, in the scene at P3, Phoebe launched a jump kick at a warlock after Paige has been knocked down by a small energy ball. Everybody else in the club was frozen by Piper, but when Phoebe lands she jostles a blonde extra who moves from her pose.
Other mistake: The one demon that knew about the 40s party was vanquished, and he went straight from spying on Paige and Phoebe at P3 to "glamouring" into Leo at the Manor. He had no way of telling Devlin about the 40s party, and yet it was still full of demons waiting to kill the Charmed Ones, with Devlin "glamoured" into Melody as a trap. And Devlin didn't even have that power - the demon that was vanquished did.
A Paige from the Past - S4-E10
Other mistake: When Piper and Leo are talking to Phoebe about Phoebe's fear of accepting Cole's marriage proposal, Piper comments "...even though he could rip your throat out with his teeth", but the closed captions mistakenly read "with is teeth." (00:05:05)
A Paige from the Past - S4-E10
Factual error: On the wall of Paige's bedroom when she was a teenager is a Metallica poster for "Garage Inc.", a CD not released until 1998 although Piper later says that Paige has gone back to 1994. (00:16:05)
A Paige from the Past - S4-E10
Factual error: When we see Paige's 1994 bedroom, she has what appears to be a Bride of Chucky doll. The movie "Bride of Chucky" wasn't released until 1998. (00:16:20)
Continuity mistake: In the teaser, Phoebe has a vision of a murder. When she first sees the shadow of the attack, the assailant is holding his victim down with his right hand while stabbing with his left. Then when the vision focuses on the Medusa head tattoo on his forearm, it is the right arm that is stabbing. (00:04:15)
Plot hole: Leo suggests to Piper that they use their magic to scare Wyke into a confession. In Ex Libris (Season 2) it is established that they can't/shouldn't use their powers to punish the guilty - even if it means saving/helping an innocent. There's no way Leo would suggest such an immoral course of action.
Other mistake: When Phoebe is trying to summon Angela the spell doesn't work and Leo says that she needs the power of three. We've seen this spell done with just one sister in the past and it's never explained why they'd need to do it together this time.
Continuity mistake: Phoebe is making her coffee and pours cream in. The next scene it's almost overflowing and black.
Charmed and Dangerous - S4-E13
Other mistake: In this episode, the Source talks about the "Ultimate Power" being the Hollow. But in Season 8, we learn that the "Ultimate Power" is Billy and Christy. (And they end up taking in the Hollow, so now are they the "Ultime Power" times 2?) Which is it? It can't be both. (00:02:05)
Charmed and Dangerous - S4-E13
Revealing mistake: In the scene where The Source uses Piper's powers together on the clay object (it blows up and then freezes), after he unfreezes it, the pieces shatter and one lands on the stand thing. As the camera moves in towards The Source, before the camera passes the clay piece it visibly vanishes (as it is CGI) and then the Source holds up a piece which is much larger and a different shape. (00:19:45)
Charmed and Dangerous - S4-E13
Revealing mistake: During the episode, Paige is wearing a sleeveless top, but when she thrown across the attic by 'The Source' the stunt double is wearing sleeves. (00:37:45)
Charmed and Dangerous - S4-E13
Revealing mistake: At the end of the episode after Phoebe and the Seer put the hollow away in its place, she leaves, but when it next cuts to a closeup of Cole, in the corner of the screen you can see her hair. (00:41:50)
Charmed and Dangerous - S4-E13
Character mistake: When Phoebe is describing to Cole the demon she saw in her premonition, she says on the good side of his face he had tribal markings, and Cole says, "Kinda like Belthazar," and Phoebe agrees. Belthazar has no markings like the ones on the demon's face.
The Three Faces of Phoebe - S4-E14
Continuity mistake: When Phoebe casts the spell to hear her hearts desire about marrying Cole it conjures old Phoebe and young Phoebe. When Leo, Piper, and Paige enter the room they all room perplexed by who the two people, just conjured, are. If this is supposed to be young Phoebe, wouldn't Leo (who has followed all them their whole lives) Piper and especially Phoebe recognize the younger Phoebe immediately instead of being confused by who she is?
Visible crew/equipment: When the Dark Priest finds the box containing the Lazarus Demon, just as the Seer says that she can always count on him to help, the shadow of the boom mic dips into view at the top of the screen. (00:09:05)
Continuity mistake: When Paige was invisible and Cole watched the blood, there was a large pool of her blood, but in the next shot, the pool of blood was smaller. (00:36:00)
Visible crew/equipment: When Phoebe tells Piper that she's on a deadline and hangs up the phone, in the next shot as Piper says that she's going to Phoebe at the newspaper, the shadow of the boom pole/mic is visible on the wall behind Piper, at the top of the screen. (00:26:45)
Plot hole: Cole explains that the demonic power is driving Karen mad because she is human. Cole later has Paige infected with one to drive her mad. This doesn't make sense since Paige is doubly not human, and shouldn't be driven mad. In fact the Charmed Ones have had demonic powers before and were not driven mad, but instead turned evil.
Suggested correction: They all are human, just not mortals.
