Prompt from sirensbane: Holmes and/or Watson meet a mythical creature.
"A dragon, Holmes, really?" Watson sat back in his chair, incredulity obvious. "If I did not know you better, I would think you were mocking me."
"Have I not told you, Watson, that when you eliminate the impossible whatever remains, however improbable, must be the truth?" Holmes calmly lit his pipe, seemingly unbothered by the fantastic nature of the tale he was relating. "And when a large reptile is flying at you, fire billowing from it's mouth, dragons suddenly seem far less improbable than they once were."
Watson stared at him quizzically for a moment, then shook his head. "I just confess, Holmes, I cannot tell if you are lying, or to what purpose you would do so. You seem to believe it, but how can I know this is not the result of a madness, like with the Devil's Foot root?"
Holmes jumped to his feet. "Quite simple, Watson. I can prove it. I will take you to the dragon, and you can see it for yourself. Then you will know it is not madness, but reality."
"If this is false," Watson warned, "you have lost all privileges of referring to my writing as romantic drivel." Despite his words, he was already clambering to his feet, willing to follow Holmes into this danger just as much as he had every other.