"No, like this," Sherlock said, yanking the violin bow away from John and demonstrating. "You have to caress the strings with the bow, not attempt to cut through them." He played a few notes before handing the violin and bow back to John, who was slightly irritated at the rude correction. He imitated Sherlock to the best of his abilities, but only managed to produce an unpleasant grating sound. Sherlock frowned.
"I'm going to have to take that away before you cause serious damage." That's exactly what he did, too.
"I'd like to see you do any better on my clarinet," John retorted.
Sherlock replied with a snort. "If you're willing to let me use it," he said. John stood up and went to his room, returning with a case. He took out his clarinet and assembled it before handing it to Sherlock, who put his fingers in the correct positions (having seen a few concert performances in his day), and produced the most awful squeak John had ever heard. He burst out laughing, which angered Sherlock.
"That's the most…hilarious thing ever," John managed between fits of laughter.
"Yeah, well, it's pointless anyway," Sherlock said, tossing the clarinet onto the couch. "Let's just stick to our own instruments in future."
