Coyote Piper - S3-E9
Revealing mistake: Prue knocked Piper unconscious in the cat fight (after the Coyote Dance), and asked Justin to carry her to the car. But when he is apparently lifting Piper up from the floor, you see Piper standing up by herself.
Coyote Piper - S3-E9
Other mistake: At the beginning of this episode, Tara and Kierken are arguing and Kierken says that he could always "suck you into your little mixing bottle and start again." Then Tara says that "she has a better idea," and then she stabs herself. The life essence automatically flows out of her but the knife was still in her body. Later, the possessed business man stabs himself in front of Piper and she kneels down to see if he was okay and the essence flew into her, without the knife being removed from his body. At the end, when Leo comes down after Prue stabs the possessed Piper, he kneels over her, but the essence does not flow into him. It only flows into him after he takes the knife out of her body.
Coyote Piper - S3-E9
Revealing mistake: After Phoebe has her premonition in the mausoleum, she wipes away the dust from the crypt to reveal Cole's father's name. Just BEFORE they show her wiping the dust away, you can see the letters in the shot of her leaning against the crypt.
Answer: "Hush, Hush, Hush" Paula Cole.