Each inhabitant of a remote village always tells the truth ...

There is this exercise in the "Discreet Mathematics" book I'm reading for my computer science course, which is leaving me scratching my head.

This one question goes like this: "Each inhabitant of a remote village always tells the truth or always lies. A villager will only give a Yes or a No response to a question a tourist asks. Suppose you are a tourist visiting this area and come to a fork in the road. One branch leads to the ruins you want to visit, the other branch leads deeper into the jungle. A villager is standing at the fork in the road. What one question can you ask the villager to determine which branch to take?"

The answer is apparently: "If I were to ask you whether the right branch leads to the ruins, would you answer yes?"

I don't quite understand why this question would reveal the correct branch to you. Can someone clear that up for me?