Shortly after moving in with Sherlock, John made a special visit to the bookstore. Unfortunately, despite the wide array of "For Dummies" books – from home renovation to yoga – it did not have the one book he needed: Deduction for Dummies. Disheartened, John made to leave before a small puzzle book, advertised as 'the best way to train your brain,' caught his eye.
A few hours later, John was sitting at the kitchen table, completing word searches, crosswords, and Sudoku puzzles with ease. The next section, simply entitled 'Spot the Differences,' proved to be significantly more difficult. Three of the differences were quite obvious: a lack of a watch, the removal of buttons, and a picture of a skull that had taken the place of an abstract painting. The fourth difference was a bit trickier: one of the books on the mantelpiece in the picture on the left was slightly thicker than its right-hand counterpart. No matter how hard he stared at it, the fifth and final difference eluded him.
The position of the teacup in proportion to his lips? No, that can't be it. Maybe it has something to do with his outfit, the pattern of his socks or something ridiculous like that. Or it could be –
"The pattern of the wallpaper."
John's internal musings stopped suddenly as he swiveled around in his chair to face the source of the comment. Sherlock was across the room, sprawled out on his usual spot on the couch, reading the newspaper.
"It's obvious, really," he continued wryly, without meeting John's gaze. "The angle at which each square meets is inconsistent on the left wall only, and the coloring is reversed."
John flipped to the back of the book where the answers were located and, sure enough, there was a large red circle drawn around the wallpaper on the left wall.
"But – how did you know that? You're not even looking at the puzzle!" John cried out, in a mix of exasperation and admiration.
"As usual John, you see but you do not observe."
John stifled a groan; clearly he was going to need more puzzle books.