"Control your mind, Potter," sneered the potions professor from across the desk. "If you have any intention of surviving an intrusion by the Dark Lord, you must. control. your mind."
"I'm trying, but it would help if you would actually try to teach me instead of just attacking me!" retorted an exasperated Harry. They had been working at occlumency for some time now, but no matter how hard he tried, Snape always broke in to his mind.
Instead of replying to Harry's accusation, Snape hissed "Legilimens."
Memories sped past, starting more recently, then moving backwards.
Harry doing a barrel roll on his Firebolt to catch the snitch to a round of applause.
Christmas at the Weasley's, with Harry receiving his new maroon sweater.
Playing wizard's chess in the Great Hall with Ron.
As the memories went further back, things became darker.
Voldemort returning in a graveyard.
Cedric Diggory's ghost asking Harry to return his body to his father.
Harry telling Cedric to take the Triwizard Cup at the same time, to share the victory…
"NO!" Harry shouted, finally ejecting Snape from his mind, but not before Snape could feel the waves of guilt washing over Harry at the last memory. Snape hadn't been aware that Harry had willingly shared the "victory" with Cedric. In fact, he was surprised that the spoiled Potter brat was willing to give up any acclaim at all.
"You're failing, Mr. Potter," he said disdainfully. This time, Harry didn't even bother with a response. He just glared.
"If you intend to keep the Dark Lord at bay, I suggest that you stop refusing to put in any effort and try to clear your mind. Now. Legilimens!"
The memories went further back.
Saving Buckbeak and Sirius in third year.
Sirius asking him to live with him.
The dementors closing in on him, a flash of green light and a woman's scream…
Snape violently withdrew his mental contact with Harry. "What was that last memory?" He asked sharply.
Harry hesitated, considering his options. He couldn't very well not answer, as Dumbledore had made it clear that no matter what, he was going to study occlumency from Snape, and he didn't want to make it harder on himself. He couldn't lie, because as the lessons proved, Snape could simply read his thoughts. After a moment, he replied. "It was my mother. Every time a dementor comes near, I hear my mother being murdered. Are you happy?" He said, jutting his chin out defiantly.
If Harry had been looking, he would have seen Snape's already pale face go a shade lighter.
"We are done for tonight, Mr. Potter. Return to your common room." Without awaiting a reply, Snape spun on his heels and strode into the lab which was attached to his office.
Slightly confused, and more than a little bit angry at being forced to remember some of his least pleasant memories, Harry stormed out of the office. Inside his lab, Snape downed a calming draught to stop his hands from shaking.