Stephen, your heartbeat says you're not being straight with Sylar here.

Not being straight with Sylar is a good way to get yourself killed.

"You know him, don't you? And as you so astutely realized, I am him. Therefore, you know me. Unless of course there's something you're not telling me."

Never mind that Sy's reasonably certain the version Stephen knows is from at least six years in the past.

Let it be known that he is disturbingly good at faking his younger self's cheerful, open innocence when he tries. The mask only cracks around the last five words or so.