At the beginning of the episode Prue's necklace disappears and then reappears. A little bit later Piper's necklace disappears.
When Leo is telling the sisters about Masselin, Phoebe is wearing only one blue necklace but then when they are at the book looking up Masselin she is wearing the same blue necklace and also another. Later in the kitchen when they are making the potion it switches back to only the blue.
Phoebe hands Piper a bowl full of stuff to add to a blender. She does so, and then turns around to talk to Phoebe. We then see the lid is on the blender, even though she never put it on. Then, she turns back around to turn on the blender, and the lid is missing. This was used as a joke in the scene, so you'd think someone would have noticed the error...
Prue says that the potion is gone and Phoebe asks if it really is and there is a close up of her skirt with a small dark stain where the potion spilled. After a cut to Phoebe getting ready to kick the door in, the stain is suddenly very light and much more spread out on her skirt.
Leo claims that he learned to use Memory Dust from another one of his witch charges. Later in the series, it's stated that this dust is actually made by Whitelighters and many of them use it.
The P3 expense numbers on Piper's laptop screen don't total up to the number in red at the bottom of the screen.