Fionn blinked a couple times before he managed to actually respond to O'Connor - he was insulted, and confused for the couple of seconds it took for him figure out what must have happened. "How stupid do you think I am? If I was the sort who spied on his own team, don't you think the last thing I'd do is tip off the paranoid homicidal psychopath and the mesh-phobic probable-killer? I had a fucking guess about what you might be thinking, and didn't want you to do something stupid - is it my fault you're an easier read than a children's book? Hell, I had you pegged before we even met Coyote, jackass."
At three hits, Clem probably notices Fionn's confusion, and the fact that he's more insulted by the accusation than anything. He doesn't appear to be hiding anything.