Pirates of the Caribbean (The Curse of the Black Pearl) - Watch Out for That Hole!
In the scene in which Jack Sparrow is fleeing from British troops (the first time, right after he saves Elizabeth), he swings around on a rope, causing a cannon to crash through the wood below him and create a huge hole to the ocean below. Look at the soldiers who "fall" into the hole. They aren't falling-- they clearly jump into it in an incredibly inconvincing manner.
Pirates of the Caribbean