Sherlock has tempered himself a bit here. He could go into her makeup, how her hair is done, what it means that she did give him the box so freely... and so on. But the deductions he made were so clearly unexpected that those would be boring by comparison.

He raises an eyebrow at her gratitude. “Really? People are not normally grateful for me being so honest, as you put it.”

Mary was. But then, she was nearly always ahead of him. She even knew Vivian would try to shoot him. And still he didn’t shut up. It’s why she’s dead. He takes a soft intake of breath at the memory.