A man is driving down a country road one evening when his car breaks down. He walks a couple of miles until he reaches a monastery. The monks there are friendly and helpful, and they give him a warm meal, a place to sleep, and a phone to call for repairs in the morning. During the night, the man hears the most unusual scratching noises coming from somewhere within the walls of the monastery, and so in the morning before the cab he calls arrives, he asks: "Last night in bed, I heard the strangest scratching sounds. Do you know what they were?" The monks all fall silent, and one steps forward and says: "Yes, we know, but we cannot tell you what they were, because you are not a monk." The man is disappointed by this, but he thanks the monks for their generosity and leaves. Ten years later, the man is traveling down the same road, and his car breaks down again. He returns to the monastery, and the monks feed him and provide a room for him to sleep in. During the night, the man hears the same strange scratching noises that he heard all those years ago, and so in the morning, he asks yet again what the noises were. The monks tell him: "We know what these noises are, but we cannot tell you, because you are not a monk." The man's curiosity is piqued and he insists that he has to know. "What must I do to become a monk, then?" the man asks. "To become a monk, you must travel the world and learn all there is to know. When you return and tell us how many grains of sand there are, and how many blades of grass there are, you can join our monastery. So, the man goes out into the world, and seventy years later, he returns to the monastery. "Have you learned how many blades of grass and grains of sand there are on Earth?" they ask him. The man knows the answer, and the monks welcome him. "Can I now know what was making those noises?" the man asks. "It is right this way," one of the monks says, and leads him to a wooden door. The man tries to open the door, but it is locked. "Can I have the key?" the man asks. "Of course," replies the monk, and he hands him the wooden key. Behind the wooden door is an iron door. This door too is locked, and the man asks for the key. The monk hands him an iron key to open the iron door, which leads to a steel door. Behind the steel door is a copper door, and then a silver door, and a gold door. This leads to doors made of ruby, emerald, sapphire, and diamond. The man asks for the key for each one, and each door is unlocked. Finally, the man comes to a door made from a strange black material. "This is the final door," says the monk, as he hands the man the final key. The man inserts the key, turns it, and pushes open the door to reveal a room, in which is sitting the source of that strange scratching sound he heard all those years ago. But I can't tell you what it is, because you're not a monk.