Au Pair II (2001)

Revealing mistake: Grandma handles the remote control in clumsy fashion, sending the model helicopter too close to the buffet and ruining the party. That's the idea at least; in truth, the cakes are catapulted in the air by devices placed under them. They are easy to spot because of the wrong timing, the geyser-like puffs of smoke they create, and you can even see marks at the bottom of a tray. (00:07:30)

Sammo