If you have children, you probably know what the tooth fairy is. Perhaps your child has caught you trying to take the tooth from under the pillow and replacing it with a coin?
This happened to me years ago. My child called out, “I caught you!” And while I was thinking how I was going to explain why I was putting a coin under the pillow and not the tooth fairy, my child said: “Put that money back. The tooth fairy left it for me!”. 😉