Sherlock wasn't afraid of dogs. He just didn't like them.
He looked down and growled at the smiling thing on the floor. His feet were pulled up and he was clutching his knees to his chest; John thought it was funny, but of course he didn't say anything. He never did. Instead, the doctor whistled, and the mutt came over for a treat.
"Why is it here?" Sherlock seethed.
"Well it was all alone on the street," John said sadly. He hoped the emotion would get Sherlock's approval, but it didn't. "Mrs. Hudson's alright with us keeping him, you know."
"You talked to Mrs. Hudson about it? Goodness, John, we're not keeping the thing."
"Come on, Sherlock, it'll be fun." John held up the dog and made a puppy face. It was a beagle, just out of puppyhood, that he'd found in the alley behind Speedy's. He fell in love with it instantly. "You're home alone a lot, you know. I'm at the clinic or on a date and you're…well, I'm not sure what you do, but I know you talk to me even though I'm away. Now you could talk to him. Mrs. Hudson did take away your skull, after all."
Sherlock scowled and eyed the thing. Mycroft had a dog. It was an ugly brute, trained to bite at any threatening situation. He still had a scar on his ankle. "You want me to take care of him?"
"You could learn," John said. He handed over the puppy; Sherlock froze and let the creature nearly fall to the floor. John caught it and situated it carefully on Sherlock's lap. "See? He likes you. It's not hard, you know. You take him outside to do him business, and you feed him every once in a while. You can play together, see?" He held up a small tennis ball. "He'll love it."
Sherlock took the ball and looked at it curiously. "What am I supposed to do with this?"
John stared blankly. "You play fetch, Sherlock."
"Fetch? Well I've already fetched it, haven't I?"
Clearing his throat, John grabbed the ball at waved it in front of the dog's face. Excited, it jumped down as John through it across the flat, and immediately returned it to its owner. "Fetch. See?" He bit his tongue. The great Sherlock Holmes doesn't know how to play fetch.
Sherlock pried the ball from the dog's mouth and grimaced at the gathering saliva. "Oh, John, the thing's a drooling idiot."
"You can dissect bodies but you can't handle a dog's spit." John shook his head and grabbed the dog. "We're keeping it. He's not stupid, Sherlock, he's just a puppy. What shall we name him?"
Sherlock thought for a moment before his eyes flickered. "Anderson."
"Sherlock."
"What?"
"Come on, I've always wanted a dog. My dad would never let me have one. Haven't you always wondered what it would be like to have a pet?"
"What purpose does a pet have?"
John shrugged in frustration. "I don't know, Sherlock, it's just there. It keeps you company; it keeps boredom away. It's something you take care of and, in a weird way, it takes care of you. Yeah, sometimes it pees on the carpet, but you love it anyway."
Sherlock took the dog and opened the door.
"What are you doing?"
"We're taking it to the pound."
"Why? Didn't you just hear what I said?"
"Of course I did." Sherlock began walking out the door. "A pet sounds lovely, but from the sound of it, I think you've already got one." He looked at John and raised his left eyebrow. "But I won't fetch."