I've been asked this.
At an organisation there are two networks. One that is for confidential information and the other is used to demonstrate things to customers. Both use RJ45 connections and the routers for each are next to one another in a room that all staff have a key to. Each office will have sockets on the wall with both networks exposed.
Now the question is this: How simple would it be for someone to connect things such that the confidential network is exposed to the open network?