The way the other man went straight for the correct drink did not escape Mycroft. It could be a coincidence, of course, but he was not a man who liked to believe in such a thing. It was more likely, he decided, that he was opposite somebody who possessed their own observational abilities. They were something that anybody had the potential for, but the general public's lack of interest in investing in them made their use notable.
How interesting. Thought a little surprising, it wasn't something that Mycroft had never come across before. Within the circles where he spent his time, the population of people making use of their senses was larger than usual as a result of the kind of work they tended to do. However, it was still worth making note of, even if only to take precautions against.
The way he poured the exact amount that Mycroft had been considering himself raised alarm bells, though. Now that was just a little too much coincidence for his liking! Were he not doing his best to ensure he gave away little of his inner thoughts, Mycroft's eyes would have narrowed at the sight. Was he being watched? It wouldn't be far from the first time that had happened, but it would be the first time he hadn't noticed.
Despite his roused suspicions, Mycroft accepted the drink anyway. He'd watched it be poured, so he knew nothing had been added to it. Of course, there was always the possibility that something had been added to the decanter before he entered the room, but the probability of that being a legitimate concern seemed minimal. If this man was smart enough to have been observing him for some time without drawing attention to himself, he would very likely be smart enough to realise how suspicious he had revealed himself to be. That meant the game currently at play was something more than a simple assassination attempt. Mycroft was being played with. Why that was, he didn't know, but what he did know was that he didn't like it.
Watching the other man drink from his own glass further reduced any worried of the drink containing anything it shouldn't, and Mycroft soon followed suit with his own sip. He had to admit, it did make him feel better. Well, he could admit that privately, anyway. Such a thing didn't feel sensible to agree with verbally.
"I'm afraid the matters weighing on my mind would be too difficult to explain to somebody not directly involved," Mycroft diplomatically responded. That wasn't a lie - he was currently working on a matter involving the cooperation of the Americans, the French, and the Russians, and getting them all to agree on anything was nigh on impossible - but his reply served more as an excuse not to reveal any real details than anything else. Obviously he didn't want to discuss his work with a stranger - especially not one who had an apparent unknown interest in him!
"What is it that you do for a living?" He asked in return, trying to extract some information of his own. The details he could observe on the other man were irritatingly lacking. He was clearly a professional, which was never good news.
Mycroft wondered what exactly he had done to deserve such a thing being set upon him. There were all manner of possibilities, of course. The most likely, based on his current work, was the Russians wanting to ensure he want double crossing them. Why, then, his tail was deciding to speak to him, Mycroft didn't know. The whole situation felt somewhat unprecedented, and that was never good.