He's suspected something for a while. Not that you were very subtle about it. There have been times where the others have noticed you dragging an unfortunate BLU to your lab and staying in there for hours. Nobody said it, but you were pretty sure they suspected something. And why shouldn't they? You ARE a cannibal, after all. But, as you're in your lab, working on your latest kill, someone FINALLY decides to confront you about it. Heavy. Of course it is. Nobody else would come near you.