Sherlock took a biscuit. He was hungry, he had clearly had a head trauma, and so putting some fuel in his body could only help him feel better. He was not afraid that Moriarty may have tampered with the biscuits, it was very hard to tamper with biscuits. And what would be the point? He had him unconscious, at his mercy, for some time and done nothing. Why bother poisoning or drugging him after the fact?

It was this miscalculation which meant he did actually take a large gulp of the tea that Moriarty brought over to him.

"The missing tube train last week, that was your work." It suddenly snapped into place from the back of his mind, a memory of seeing the small piece in the paper about it. "A rolling base, very clever. Where is it kept when you're not using it?"