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.
Revealing mistake: When Prue is practising using her powers while astral projecting, when Phoebe walks away to go see her in the attack you can see the makeup they used in an attempt to hide her tattoo on the right side of her back. It looks as though she's been bruised there. (00:00:43)
Siren Song - S5-E4
Character mistake: When discussing how best to help Melissa, Piper tells Paige that her birth father was half whitelighter, when he was fully a whitelighter. (00:25:15)
Revealing mistake: The character Ramus (the elder) changes actor when Leo jumps and orbs to get him away from the attack of the Aggressor. The actor's stand-in is visible instead. (00:18:52)
Sympathy for the Demon - S5-E7
Visible crew/equipment: After Paige orbs the potion onto Barbas and Cole absorbs all the powers, in the shot of Barbas getting up from the floor we can see a blue T-mark and an orange T-mark taped to the rug. (00:39:05)
Continuity mistake: Leo says that Piper's past lover is his past life. If it was a past life, in 1924, that means Leo must have died almost straight away to be old enough to qualify as a doctor in WW2. And it wouldn't be his past life but his own past if it was the same life from before he became a Whitelighter. But then he'd also have been 15-20 years older before he died in WW2.
Continuity mistake: In the church scene when Phoebe and Piper are showing Paige how to use her power, Piper says "according to the prophecy, the third sister has the power to move things with her mind, like Prue could." Prue was not the third sister, but the first. Paige is technically The Fourth Sister, but since the prophecy didn't speak of a "Power of Four", she would automatically become the third sister after Prue's death. (01:02:42)
Witch Wars - S6-E21
Continuity mistake: When Paige goes to The Bay Mirror to bring Phoebe potions we see she has 3 different colored potions: green, blue, and orange. She hands the light blue "explosive" to Phoebe, then hands the green one saying it's "acid" but when she hands Phoebe the last potion the camera angle changes and we see that she's again handing her the green one. At this time we see that Phoebe is holding the blue and the orange ones. (00:10:28)
Wicca Envy - S1-E10
Audio problem: When talking about the tiara with a security guard Prue's mouth stops moving mid sentence but the audio continues.
Other mistake: This entire episode the ghost brothers whine that Leo is responsible for them dying and he left them to die, even Leo believes this. It makes no sense. As we see in the flashback even if Leo stayed to help they were blown up moments later and still would have died.
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?
Crimes and Witch-Demeanors - S6-E19
Visible crew/equipment: After the opening credits, in the first shot Phoebe is at the stove, then when she turns to walk toward the Book of Shadows we can see the pink T-mark taped to the crew's black mat at the bottom of the screen, which will be where Chris stands shortly. (00:03:25)
The Legend of Sleepy Halliwell - S6-E14
Visible crew/equipment: When Leo and the sisters enter the great hall we hear Gideon call to Leo and thank him for coming, then as the camera pans to the left we can see the T-mark on the floor, at the bottom left corner of the screen. (00:09:25)
Valhalley of the Dolls (1) - S6-E1
Visible crew/equipment: When Chris tells Phoebe that Paige erased Piper's memory, Phoebe shouts Paige's name then walks away from Piper, and in the next shot we can see two pink T-marks taped to the floor under the table, where Paige is holding Wyatt. (00:27:05)
Visible crew/equipment: While Elise is telling everyone about Bay Mirror's new owner, Jason Dean, just as she warns them that he's known for shaking up companies, we can see the white T-mark and a bit of the yellow tape mark on the crew's black mat (which is gone in following shots) at the lower left of the screen. (00:09:15)
The Day The Magic Died - S5-E15
Visible crew/equipment: While Phoebe and Paige are in the kitchen with the unicorn they realise they've lost their powers, and when Leo joins the sisters in the kitchen we can see two animal handlers - one wearing a short sleeved white shirt behind the animal, and another holding the rope hiding under the table. (00:10:35)
The Day The Magic Died - S5-E15
Visible crew/equipment: While Paige and Phoebe are in the basement getting some magic from the unicorn horn, Phoebe figures out it was the Elders who sent the unicorn, and just as Paige comments that the unicorn's magic is not affected by what happens on Earth, you can see the animal handler's hand under the animal's muzzle. (00:37:35)
Sand Francisco Dreamin' - S5-E14
Visible crew/equipment: After Phoebe returns with a bowl of dream dust from the remains of the Sandman, Phoebe opens and closes the door to the conservatory to view their three dream guests, then as they all turn and walk toward the sofa we can see the reflection of the moving boom pole and mic in the mirror. Also, note the door that Phoebe had closed is now wide open in Leo's closeups. (00:32:15)
House Call - S5-E13
Continuity mistake: When Leo finds Piper on the ladder removing the "filthy" wood shingles he's wearing a crew-neck grey and blue pullover, but when Piper climbs off the ladder and Leo tells her she needs to snap out of it Leo is wearing something beige with a collar, then it's back to the crew-neck pullover. (00:31:00)
Visible crew/equipment: After Bacarra takes the human heart from the witch it cuts to the Halliwell manor, and as the camera pans to the right we can see lighting equipment and the boom mic (with a white striped tip) at the top of the screen, then in a following shot from the same direction the boom mic is visible again. (00:30:55)
Answer: "Hush, Hush, Hush" Paula Cole.