“The paint’s supposed to go where?” John stared incredulously at Sherlock, brush in his hand.
Sherlock huffed. "It’s performance art. And there are certain parts of my anatomy I can’t reach well.”
John shook his head. He never did understand everything Sherlock asked of him, and this was no exception. Crouching a bit, tongue sticking to the corner of his mouth, he painted a rough aproximation of a tree in the middle of Sherlock’s back, then painted roots going down…
“i don’t know if I can do this,” muttered John.
“I’ll let you help me wash it off when we’re done,” said Sherlock without turning around.
“How do you know I actually painted what you wanted back here, anyway?”
“Because you did.” Sherlock stayed perfectly still.
John looked at his work, adding a few finishing strokes. Wasn’t that the sum of their friendship? Sherlock didn’t have to second guess, John simply did and that was enough for them.