One of my favorite Smullyan works is the lesser-known 5000 B.C. and Other Philosophical Fantasies. Here's one of the more amusing anecdotes from that book:

In item #249 of my book of logic puzzles titled What Is the Name of This Book?, I describe an infallible method of proving anything whatsoever. Only a magician is capable of employing the method, however. I once used it on [noted philosopher] Rudolph Carnap to prove the existence of God.

"Here you see a red card," I said to Professor Carnap as I removed a card from the deck. "I place it face down in your palm. Now you know that a false proposition implies any proposition. Therefore, if this card were black, then God would exist. Do you agree?"

"Oh, certainly," replied Carnap, "if the card were black, then God would exist."

"Very good," I said as I turned over the card. "As you see, the card is black. Therefore, God exists!"

"Ah yes!" replied Carnap in a philosophical tone. "Proof by legerdemain! Same as the theologians use!"