The boys, the "terrible trio", are walking along the beach after Hermie's first encounter with Dorothy. Her house is in the background. After a while, the scene cuts and they are back where they started.
When Dorothy is drinking coffee with Hermie in their introductory scene, she holds the cup in her right hand, with her left hand elevating the saucer under it (British formal tea style). But the reverse angle shows her holding the cup with both hands and the saucer has vanished.