When Prue is up in the attic saying the spell that makes three of her phoebe and Piper are downstairs. Look at Piper's hair it's clearly down. The spell makes a loud noise after being cast and Piper and phobe race up the stairs, you'll notice Piper's hair is still down yet when the camera cuts away into the attic to catch the two storming in Piper now has a very nice ponytail going. Where in the split-second it took for them to walk through the doorway did she manage to pull her hair back into a neatly coifed do? Especially when considering that while she was wearing bracelets none of them appeared to be hair elastics.