She can see his blush threatening to creep right on down his neck when she does it again. This time he makes a rather undignified noise of surprise. Briefly. And quietly. He wasn't expecting that.

"I-i. Well, uhm." He sucks in a deep breath. "Yes. Per cup, one gets more caffeine out of coffee and I like it old and/or reheated much better than old tea." And when cases get really bad he just makes double strength coffee that tastes awful but has enough caffeine to get the job done.