The Monks’ Secret

A man is driving down the road and his car breaks down near a monastery. He goes to the monastery, knocks on the door and tells them that he has a problem with this car. ‘Do you think I could stay the night?’ he asks. The monks are happy to help him. They give him dinner and tell him he can stay for the night.
Before the man falls asleep, he hears a very strange sound. A sound he had never heard before. The next morning, he asks the monks what the sound was, but they say: ‘We can't tell you. You're not a monk.’ The man is disappointed, but he thanks the monks because they also fixed his car before he got up. The man says goodbye and leaves.
Some years later, the same man is driving in front of the same monastery and his car breaks down again. The monks again accept him, feed him, and give him a bed for the night. That night, he hears the same strange noise that he had heard years earlier. The next morning, he asks what it is, but the monks reply: ‘We can't tell you. You're not a monk.’
The man says, ‘All right, all right. I'm dying to know. So, how do I become a monk?’ The monks tell him that he has to travel the earth and tell them how many blades of grass there are and the exact number of stones there are. ‘When you find these numbers, you will become a monk’, they said. The man decides to do it.
Almost 51 years later, he returns and knocks on the door of the monastery. He says, ‘I have travelled the earth and have found what you have asked for. There are 2431,107,985,647 blades of grass and 801, 221,707,451,447,658 stones on the earth.’ The monks are surprised. ‘Congratulations. You are now a monk,’ they say. ‘We will now show you the way to the sound.’ The monks take the man to a wooden door where the head monk says: ‘The sound is behind that door.’ The man reaches for the door handle, but the door is locked.
‘Really funny,’ says the man,‘ but please give me the key.’ The monks give him the key, and he opens the door. Behind the wooden door is another door made of stone. The man asks for the key to the stone door. The monks give him the key and he opens it. Behind that door is another door made of gold. He asks for another key from the monks, who give it to him. Behind that door is another door and this one is made of diamond. And this went on until the man had gone through all the doors. Finally, the monks say, this is the last key to the last door.
The man is excited to know that he has finally reached the end. He unlocks the door, turns the handle, and behind that door he is amazed to finally see the reason for that strange sound.
But he cannot tell you what it is; because you're not a monk.