In a spy novel I had just read, the hero hid a letter in a particular statue in Washington, D.C. 

Since I was in that city at the time, on a whim I decided to see if the statue really contained the small niche the author had described. 

To my great surprise, it did — and a cellophane-wrapped letter was inside. After a moment’s hesitation, I pulled out the letter, opened it, and burst into laughter.

An unidentified reader had penned, “Good book, wasn’t it?”

One Liner
Nothing is so embarrassing as watching someone do something that you said couldn’t be done.