Crockett Johnson/ published 1959 by Harper & Row
Growing up, I was familiar with Harold and the Purple Crayon (if for no other reason that it resembled my favorite Captain Kangaroo bit -- Simon in the Land of Chalk Drawings).
It was only after I had my son that I came to realize Harold had way more than one adventure (Harold's Fairy Tale/Trip to the Sky/at the North Pole/ABC/etc.) And this "astounding, colossal, purple crayon event" about Harold at the circus.
It was the tail of a lion.
Somehow a lion had gotten loose in the circus.
Before anyone could quite recognize the
danger and become alarmed, Harold
was at work getting the lion into the cage.
He got into the cage himself, with nothing
but a lion tamer's chair.
Then, like the bravest of lion tamers, he faced the lion.
With no thought of fear, he put his head right in the lion's mouth.
After he took his head out of the lion's mouth
it occurred to him that lions have big teeth.
That last part is my favorite, as we see Harold drawing in the lion's teeth even as his face grows blank with fear. Every book in this series is such a vivid illustration of the wonders of a child's imagination. Really, anything by Mr. Johnson or his wife Ruth gets a million thumbs up in my book.
The Happy Egg