You’re just thick. The Doctor’s answer is warmer in response to that chuckle. He waits while the Master explores the memories.

Obviously it is, is his solemn answer to the Master’s denial, even though he fully agrees. Because how many other things has he seen in his life that logic, reason, and all his experience told him were impossible? –That’s why I keep traveling, he’d told someone once, before taking a leap of faith into a dark pit on a planet that couldn’t exist, looking for a creature he didn’t believe in. To be proved wrong.–

He doesn’t make a particular effort to hide any of his thoughts from the other.