When Phoebe is in the kitchen pouring her coffee, she pours the coffee into the only mug sitting visibly on the counter. In the next shot, she is holding a mug but the mug she poured her coffee into is sitting exactly where it was when she poured the coffee.
After Phoebe has her premonition of the attic scene, they remark that Ava wasn't in the premonition. Except if you look closely at the premonition scene, you can clearly see Ava standing next to Paige by the Book of Shadows. She's wearing a long-sleeved white blouse, which none of the other characters wear.
Leo brings home a video about home birthing, but when he and Piper are watching the video, it's clear that the birth is taking place in a hospital (mother in a hospital gown, an IV, etc.)
You can clearly see that Madam Teresa's markings are already on Phoebe's hand when she first enters the shop, and when she firsts sits down. Obviously the takes had to be redone, because when she does draw on her hand eventually, they aren't there anymore (first take perhaps).
When Paige tells Piper about Theresa being killed, she says "Madam Theresa was murdered" and places emphasis on "was" - as if they weren't sure. They had no reason to suspect she was even in danger of being attacked at all.
After Piper gets her blood drawn, the person drawing it takes the needle out and turns around without having anything over where the needle was to soak up the blood. In reality, he would have put a piece of gauze there before pulling the needle out so there would be no chance of blood dripping (and no one to see Piper heal.)
In the beginning of the episode, when Lydia is on the phone with Teresa, she speaks with a Romanian accent. Later on, when she is teaching Paige and Phoebe about the tea leaves, she no longer has an accent.