After Piper says Leo can't see her baby photo, Leo tells Piper he's been watching over her and her sisters their whole lives. Previously he has had to ask what happened before he met them (for example Prue's car accident at 18 in Murphy's Luck.)
A shot from outside Halliwell manor shows Leo leaning out of a round window, but in the next shot from inside, the window is octagonal. Leo's size in the outside shot is also disproportionate to his actual size, as he appears taller than the entire front door.
Phoebe signs her name on the divorce papers as 'Pheobe'.
When Phoebe is a mermaid she is worried about getting her hair wet but before she finally goes under the water it appears that her hair is already wet.