Can anyone help me name this book

[peppercorn]

As a child I read a book about a boy who had to do three things 1. Show something that no-one in the world had ever seen before. 2. Something that this person (the one in the book) could do. 3. Tell the same person what he was thinking. He achieved all three and for some unknown reason it has remained with me all of my life, but I don't know the name of the book and I would love to read it again. Can anyone help?

[peppercorn]

sorry should have said something he couldn't do!