John is very aware of Sherlock's studious gaze, having been subject to its overbearing weight more often than he'd like. Whatever Sherlock assumes about him is probably right, but John would much rather direct the conversation away from that and to something more productive and less embarrassing, and hopefully more distracting.

He bends close to look at the photographs again, trying and failing to discern something new, though he finds himself wholly ineffective and completely distracted. What if he'd squeezed just a little tighter? What if he'd not let go at all? Surely Sherlock would know when things were getting dangerous, wouldn't he? He wouldn't intentionally hurt John like that. But there was always that possibility.

John swallows hard -- an unconscious motion and picked up another photograph to force himself to study it. They were faint... but there were definitely markings. "These wrists must've also been tied up," he notes, showing Sherlock. "Not with bed straps, either, which is common in aggressive or patients with a tendency to hurt themselves. It's too thin. Matches the rope round the neck if you look closely enough." John frowns and shakes his head. "Maybe our paranoid patient isn't so out of his mind after all."