Continuity mistake: Paige looks in the Book of Shadows and suggests that the demon they are looking for could be Belthazor, not knowing that Belthazor is Cole's demonic form. But we saw Phoebe making extensive changes to Belthazor's entry in the Book of Shadows in a previous episode, and the changes are not in evidence here. (00:01:40)
Revealing mistake: When Paige cuts the flesh away from Sykes, you can visibly see a white bandage-like thing under his skin as it comes off. (00:23:20)
Plot hole: After Cole explains he might not be able to regain control after embracing his demonic half, he tells Phoebe she should have the Belthazor vanquish potion ready just in case. But in "Look Who's Barking", Piper tried using that potion on Cole and it didn't work because he had himself magically protected from it. (00:27:15)
Continuity mistake: After Phoebe finds the Scavenger Demon page in the Book of Shadows the camera dollies out, and when Piper asks what happened with Cole, the crew's taped black mat is visible on the bare floor with no fringed area rug, then when Cole shimmers into the attic, in the next shot of Piper and Phoebe we see the fringed area rug at the bottom of the screen. (00:06:35)
Visible crew/equipment: When Sykes is about to kill Susan at the ADA'S office, Leo hits Sykes and orbs out with Susan, and in the next shot as Sykes sits up we can see the green tape mark on the floor, under his leg. (00:22:30)
Continuity mistake: When Phoebe tries talking to Emma about Belthazor, Emma's hands are folded in front of her, holding her sweater closed. In the following shot when Emma turns around, her arms are now down by her sides, with her sweater open. (00:31:10)
Answer: "Hush, Hush, Hush" Paula Cole.