Harry lasted just over an hour. By that time, he was nearly delirious with heat and exhaustion, and not eating breakfast hadn't done him any favours. He thought the fire was getting hotter, and he kept scrubbing the same place on the floor, and he could have sworn Snape was staring at him, which wasn't helping.
Sinking back on his heels, Harry blinked the sweat out of his eyes and rubbed at his forehead with his arm. He swayed alarmingly when he opened his eyes again, the room spinning, and he threw his other hand out to catch himself. Once he was steady, he glanced up at Snape to see if he'd noticed; the last thing he needed was for Snape to think he couldn't handle a little work. It wasn't like the Dursleys didn't make him clean things all the time, and Snape had another thing coming if he thought Harry couldn't clean his stupid floor. But when he looked at Snape, Snape was looking somewhere else, just like he had been every other time Harry had checked.
Harry shot him a glare and then yanked his jumper over his head. He hated admitting defeat, but he was worried he might pass out if he didn't cool down somehow. Cursing Snape in his mind, he balled up the jumper and threw it at the chair. Then he heard movement behind him, the slide of Snape's chair against the dungeon floor, the soft whisper of his robes as he moved. Harry risked another look and saw that Snape was standing with his back to Harry, one shoulder leaning casually against the wall, the other arm moving slightly as he flipped through a book.
A surge of anger tore through Harry, that Snape could be so maddeningly casual, so cool and calm and collected in this hell of a dungeon. Harry could just see the edges of his profile, and there wasn't a drop of sweat in that greasy hair. He bared his teeth and then Snape—moved, somehow, turned and shifted closer to the wall, and Harry was almost knocked over by the image of himself, caught between Snape and the wall, clutching at Snape's shoulders and grinding against his thigh the way he had last night.
The room was suddenly much hotter.
Without thinking about it, Harry pulled off his glasses, yanked his t-shirt over his head, used it to wipe the sweat from his face, and then threw it at the chair with his jumper. He put his glasses back on and threw himself into scrubbing the floor, determined to lose himself in the work, in the stretch and ache of his muscles, in anything that wasn't Snape.
It worked for a while. But as Harry cleaned, he gradually became aware of that prickling sensation on the back of his neck, the one that meant Snape was watching him. It took him a few minutes to realise that it wasn't going away. Snape wasn't glancing at him occasionally. Snape wasn't just checking up on him to make sure he was still working. Snape was staring at him, and there was Harry, on all fours and shirtless and sweaty.
Tension coiled between his shoulders at the thought. He couldn't imagine any reason Snape would be staring at him, unless he was doing something wrong. And if he was doing something wrong, Snape would say so, often and with big words. That left only the possibility that Snape was watching him to make him uncomfortable, to distract him into messing up so he'd have to start all over.
Well, he wouldn't. Harry set his jaw, plunged the rag into the bucket, and then attacked the floor with renewed force. Ignoring Snape's eyes on him, though, was a lot harder than he'd expected. They were burning into him, as if the dungeon wasn't already hot enough, and it didn't take long for Harry's skin to start tingling, every inch of him aware of Snape's presence.
And thinking about Snape's presence only got him thinking about the night before, when he'd been so overwhelmed by that presence, by all that heat and pressure, that he'd forgotten himself completely. And now there was more heat and a different kind of pressure, and to his horror, Harry's cock started to harden. He scrubbed more vigourously at the floor and tried not to slip on his own sweat.
Harry felt near collapse by the time lunch rolled around; pain was shooting through his knees every time he moved, his back and shoulders were aching, his hands had been rubbed raw, and his cock was so hard it hurt. But at least there was no way Snape was going to be able to complain about his stupid floor, or anything else in the dungeon. It was spotless. Harry was sure of it.
Harry hated this, hated that he reacted to Snape this way despite his hatred, and he wondered if Snape had been telling the truth the night before, about hatred not mattering. It hadn't seemed to matter much when he'd brought himself off against Snape's leg, and that was... really not what he needed to be thinking about.
Snape finally barked that it was time for lunch, and Harry gratefully straightened and stretched, trying to ease his aching muscles. He was still hard, and he was careful to keep his back to Snape as he walked awkwardly to the armchair to get his shirt. He wrinkled his nose as he realised how sweat-soaked he was, and used his jumper to dry himself before pulling on his t-shirt. For once he was grateful to be wearing Dudley's giant hand-me-downs; at least there was some chance Snape wouldn't notice the tent in his trousers. He was far too hot to even think about putting the jumper back on, so he left it where it was.
He left the office as quickly as he could, not bothering to wait for Snape. But he'd only just made it outside when he was stopped in his tracks by the cool air in the corridors; it was such a relief after the sweltering heat of Snape's office that he froze and closed his eyes, letting the very slight dungeon breeze waft over him. He'd never noticed it before, and it felt so good he almost smiled.
He was startled out of his reverie when Snape's office door slammed shut a few moments later. He stayed where he was for another second or two, and then headed for the Great Hall without so much as a backwards glance at Snape.
'Harry, what have you been doing?' It was Hermione's turn to look outraged.
'Cleaning Snape's office,' Harry said, piling his plate full of food and not bothering to lower his voice.
Ron elbowed him in the ribs. 'He'll hear you!'
Harry rolled his eyes and glanced quickly at Snape, who was at the other end of the table, ignoring everyone. 'It's not like he doesn't know what I've been doing, Ron.'
Ron's ears turned a little red. 'Yeah...'
'Look, I don't want to talk about it. It's bad enough I have to be there all day. How's the research going?'
After lunch, Harry followed Snape back to his office and tried to control his nerves. There was a lot more time between lunch and supper than there was between breakfast and lunch, and although Snape had said he could study, Harry didn't trust him. He watched apprehensively as Snape put his palm on the door and the wards shimmered away, and then he waited for Snape to wave him inside.
It was like walking into a furnace. Harry hadn't realised how hot the room had become, but after being in the Great Hall, it was almost unbearable. He looked at Snape, who seemed unaffected.
'Why aren't you hot?' he demanded. 'Sir.'
Snape's head swiveled around and he arched an eyebrow. 'Cooling charms on my robes.'
Harry felt his mouth drop open. 'That's not fair!'
The eyebrow climbed a little higher. 'Fair? I rather think the word you're looking for is pleasant. Because punishments aren't pleasant, Mr Potter, but they are always fair.'
Harry sighed and shook his head slightly, not really in the mood to listen to Snape's weird life lessons. He shoved the fringe off his forehead, which was already starting to sweat, and changed the subject. 'Can I—you said I could study after lunch, Professor.' He tried to keep his tone respectful. 'Is it all right if I just read, sir?'
He hoped so; he was exhausted, so tired he could barely see straight, and he wasn't sure he'd make it through another hour of physical labour. Snape shot another sceptical glance at his books, but inclined his head. 'Very well. It should at least keep you out of my way while I test the potion.'
Harry bit back his sigh of relief and curled back up on the chair to read.
Five minutes later he was wishing heroic hippogriffs were more interesting. Between the exhaustion, the heat, and the huge lunch he'd eaten, Harry was having trouble keeping his eyes open. And when they were open, he was having trouble concentrating on the words in front of him. They swam in and out of focus, and Harry's eyelids felt made of lead, and he was only dimly aware of the book sliding from his fingertips as he fell asleep.