"Watson?" Sherlock Holmes asked, "may I trouble you for a bit of your professional knowledge?"
"Of course," Watson agreed. "What would you like to know?"
"Have you ever seen the victim of an animal attack?"
A cloud passed over Watson's features for just a moment before he answered. "I have," he said stoically. "I've seen children mauled by dogs and soldiers mauled by tigers. One bear attack, not much more beyond that."
"And how could you know it really was an animal?" Holmes asked. "If the victim was dead, I mean? Would there be anything that told you it wasn't a very clever murderer?" Sherlock Holmes himself was hunched over a text, studying it seemingly intently though Watson knew there were very few things he wasn't noticing.
"Yes, there are a couple ways to know," Watson said, his voice slipping easily into a teaching cadence. "Allow me a moment, and I will illustrate the point."
Sherlock Holmes wasn't quite expecting Watson to literally illustrate, but that was exactly what he got. He put his own text away and watched as Watson rummaged through a notebook that Holmes quickly realized was actually a sketchbook, pulling out several drawings.
"Take a look at this," Watson said, handing over a large, slightly yellowed page. On it, there was a grotesque yet clinical and anatomically perfect pencil sketch of a man's neck, the flesh ripped and bone visible underneath.
Watson sat next to him, showing him how and where predator animals like tigers would bite their prey. They wouldn't often use their claws to kill, Watson explained, that the real deadly wound would instead come from their incredible bite force and neck musculature. It would be incredibly hard, therefore, for a human antagonist to recreate that kind of wound.
"Even wounds from an animal's claw have a specific look," he explained, passing Holmes another drawing. This one showed a man's torso, four long slashes ripping through his flesh. "See how it's ripped and torn?" Watson asked. "It's very hard to recreate that with a knife. And even if someone could, if they had a claw, perhaps, most people still wouldn't be able to recreate a convincing mark." He pointed out the beginning of the slashes and how they were different then the ends and how the depth varied.
He pulled another drawing out as he talked, his speech falling away as he glanced at it. He cleared his throat. "Another thing about animal attacks," he said sadly, "is that they're not typically random. They're calculated. People think of animals as savages, of nature red in tooth and claw, of attacks as violent, loud, bloody things, but the truth is that you walk out in the morning to a ripped tent and a grown man is simply gone. You'll find a shoe, sometimes, or a couple spots of blood, but the truth is they're very quiet affairs."
He didn't quite realize that Holmes had laid his hand on his wrist and was looking at him with something that might have been kindness and might have been concern.
"I didn't know you could draw so well," Holmes said. "You're a man of hidden talents, Watson."
Watson blinked a bit, pushed the papers away.
"I have a corpse to attend to later today," Holmes continued. "That is why I was studying: there's some question, apparently, about the cause of death, and my personal experience doesn't extend far beyond canines. Will you come with me?"
"Of course I will," Watson answered, shaking off the memories, swiping the drawings back into their notebook, and rising.
Sherlock Holmes watched him, then rose as well. He didn't quite know how personal some of what Watson had just shared may be, but he was very glad that, whatever the doctor had been through, that he had ended up in Baker Street.
For the prompt from Hades Lord of the Dead: Watson's secret talent
With prompt like that, a prequel to the first story just seemed appropriate.