The halloween party that Aaron invites Cady to which is supposedly at his friend Chris's house is the same exact house that Cady throws her party at which is supposedly her house. If you notice, when Cady walks through the front door of the halloween party, you see the steps on the right and the banister with white railings making the hallway at the top of the stairs visable. You also see the "kitchen" straight ahead, (and you can tell they tried in every way possible to make it look like it wasn't the same kitchen by stuffing lots of people in it) and a door off to the left leading to the living room. At cady's party, when people walk through the front door, you can clearly see the stairs, the banister at the top of the stairs, the kitchen..and the door leading to the living room off to the left.