Draco felt that moment when Potter's wall fell, when the memory was about to burst over him. He thought, for the briefest moment, to withdraw and give him time to regroup, but no... Harry would learn better if Draco pushed onward, forced him to relive it. If Draco pushed at him.
Then the memory struck and Draco couldn't pull away if he tried, trapped by his own echo of this same scene, the one time Potter had seen him vulnerable. This was one of those moments when Draco had let his walls down, had indulged in the feelings he kept locked away at all other times. And Potter, of all people, had witnessed him, and nearly killed him after.
He saw the shift, felt that twist in Potter's mind as the memory changed. His chest echoed a cold pain, and Draco's eyes closed, the contact between them severed as his wand hand dropped. He didn't touch his chest and abdomen where a thick silver tracery of scars remained from that day. His breathing came rough and ragged, voice hoarse as he smiled tightly. "Very good, Potter. If I didn't know better, I might believe it."
Draco set the wand down on the bed, well within Potter's reach, then pushed himself to standing and walked away. It took him a moment to put his own mind back together, wrapping himself in calm once more. "I think you've learned enough today to spend some time on your own implementing the lesson." When he turned back to face him, he arched one eyebrow. "Homework. Take your memories of the brandings and put them away securely, over and over, until they slip into their boxes at a thought. Do that with what you leave out. I have every faith that you are capable of this."