"… and thus we can conclude that our murderer did not in fact take the Tube to the crime scene, but instead – Yellow Car – walked there from Wilkinson Road, after having stopped at a newsagent's to buy –"
"Sorry? What did you say?" John bats his eyelashes innocently at Sherlock.
"The murderer walked six miles before killing the girl. Can you actually hear me when I'm talking or are you just watching my lips move?"
"No. Before that."
"The girl had no reason to be at the crime scene. You can tell from her shirt and her handbag that she had a dental appointment at four o'clock, which, judging by her shoes and the fact that she lived in Northeast London, must have been at least ten miles away from the crime scene. Chances are that her murderer lured her out there by using an expensive kind of perfume and faking a phone call at her cousin's best friend's house."
"Very nice deduction and all that, very impressive, buuut … I didn't mean that."
Silence for a moment. Sherlock turns his back to John and watches the oncoming traffic.
"Yellow Car." Sherlock's eyes widen in surprise and he clenches his teeth.
"Sorry?" John is working very hard to suppress a manic giggle.
"Hmm? I didn't say anything," Sherlock mutters with a distant look in his eyes.
"I think you did," John snickers.
Ten more minutes are passed in complete silence, John grinning mischievously and glancing at Sherlock from time to time, said other man staring outside the cab window absent-mindedly.
On the other side of the road, there is a replica of a New York Yellow Cab, and John notices it before Sherlock does, which is quite unusual, but then again their whole situation is rather surreal. John looks over at his friend and waits for the inevitable. There is a slight twitch in Sherlock's upper lip, and before he can control his impulse there it is: "Yellow Car," in a clear but monotonous voice and punctuated by an angry glare. It is followed by a sudden outburst of laughter from the other side of the taxi, which is only cut short by Sherlock digging his nails into John's wrist and hissing at him, "If you don't tell me how you did this I can easily make you unconscious with my bare hands!"
Tears of laughter start running from John's eyes and he can barely catch his breath to try and explain the situation. "Remember when … Hahaha, um, sorry … you know when –" he manages to splutter between giggles, but is interrupted when Sherlock succumbs to the mysterious urge to point out another yellow vehicle again.
"Ahem. Yes, sorry. Remember when I tried to hypnotize you so you wouldn't talk as much? And you threw a book at my head and said I wasn't a trained hypnotist?" Sherlock huffs indignantly, but lets his friend continue.
"Well, actually a friend who is a psychologist taught me this trick. Her brother wouldn't play "Yellow Car" with her on a long drive so she figured out a way to make him … I didn't know if it would work, but this – never thought it would be so much fun!"
The icy glare Sherlock has been giving John transforms into the pout of a five-year-old. "Hypnosis is very dangerous to play around with. I honestly can't believe you would do such a thing to me!"
John shoves the taller man out of the taxi and towards the door of 221B Baker Street before any more yellow cars can pass them by.
"Oh, shut up, you whiny baby. I know how to reverse the hypnosis. And look at the bright side – at least now we know you're not colour-blind!"