"It does, as a matter of fact," the Doctor replied. He found his voice had lowered, just the slightest bit, and he was finding his mind surprisingly non-distracted. Jack was focusing him on the situation, focusing him on every word and every movement. He followed his eyes where Jack looked and felt his skin flush as though he'd been touched.

Jack was very, very good at this.

"Reaction," the Doctor said. It came out as a squeaky breath, and he quickly and quietly cleared his throat. "Reaction," he said, more firmly. "T-That's the whole point of a proper experiment, though."