I put my vote on christoph
^ was thinking that and dreading it. christoph was the one who made the drink or at least helped kyon make it, and the fact s2 opens with christoph *experiencing a strange ringing in his ears* kinda points to him being suspicious.
thing is, christoph's been there for ages yet cecilia, who just arrived, had to be involved. i wonder if she's pinning blame on him just possibly, though the drink would be hard to explain.
Thanks for the meal