It probably says a lot about Rodolphus that he stops immediately, jerking around to see who or what touched him. He hardly expects an attack in the guild hall, but he's also been around long enough that people know he's not particularly friendly, so this is unheard of for him. Unlike someone else, too, he doesn't waste any time doubting what he felt or questioning himself — he never does that in matters like this.

Upon failing to perceive anything obvious, he pauses, then removes his wand. He makes one terse gesture with it, but nothing appears to happen. He tries another, and something does happen, but it's only visible to him and he has no noticeable reaction — analyzing the amount of magic in the immediate area does not tell him much, thanks to Hellsing's extensive wards. Having at least established there is no obvious unusual magical intrusion, he considers his options. He is totally just standing there staring at a wall (not in Dean's direction), thinking.