Harry did not bother to nod. He knew all of this already.
“More recently,” said Dumbledore, “I became concerned that Voldemort might realise that this connection between you exists. Sure enough, there came a time when you entered so far into his mind and thoughts that he sensed your presence. I am speaking, of course, of the night when you witnessed the attack on Mr. Weasley—”
“Yeah, Snape told me,” Harry muttered.
“Professor Snape, Harry,” Dumbledore corrected him quietly. “But did you not wonder why it was not I who explained this to you? Why I did not teach you Occlumency? Why I had not so much as looked at you for months?”
Harry looked up. He could see now that Dumbledore looked sad and tired.
“Yeah,” Harry mumbled. “Yeah, I wondered.”
“You see,” Dumbledore continued, “I believed it could not be long before Voldemort attempted to force his way into your mind, to manipulate and misdirect your thoughts, and I was not eager to give him more incentives to do so. I was sure that if he realised that our relationship was—or had ever been—closer than that of headmaster and pupil, he would seize his chance to use you as a means to spy on me. I feared the uses to which he would put you, the possibility that he might try and possess you. Harry, I believe I was right to think that Voldemort would have made use of you in such a way. On those rare occasions when we had close contact, I thought I saw a shadow of him stir behind your eyes…