Disclaimer: None of it is mine, it all belongs to JKR! (particularly any lines recognizable from HBP and DH, which I've tried to italicize).
He couldn't breathe, couldn't think; the snake was gone-he had felt the cold and pain as it released its grip on him, heard the solid slide of it against the shack's rough floor-but in its place was agony at his neck, radiating down his shoulder and arm and chest. He pressed one palm flat against his neck, or tried to; from the blood pumping eagerly through his fingers, he knew that his muscles were already weakened. His other hand scrabbled blindly against the dirty floor as wave after wave of pain drew over him.
Dimly, Severus was aware that he had failed in the end, failed spectacularly when he was so close. Potter, he thought, and then nothing, another wave of pain driving even his failures away from him.
There was an unpleasant thudding and shuffling sound, and he opened his eyes, the fingers of his right hand clenching against the floorboards. Had he the strength, he would have shouted in surprise; looming above him, as if conjured by his half-formed thoughts, was Potter, dirty, untidy, bewildered-looking as ever. He opened his mouth as if to say something, but Snape forestalled him, his sluggish brain catching on-he still had a chance!-and with a supreme effort that he would have thought himself incapable of only seconds before, he reached up and grabbed Potter by the front of his robes.
Ignoring the boy's startled expression, Severus drew in a deep breath, feeling as though shards of glass were tearing through the tendons of his neck, and without conscious thought, sought to expel the memories he needed Potter to see. He had never attempted this without a wand before, and it was with vague alarm that he realized the slimy substance creeping from his ears, nose and mouth were his memories, and he had no way to hold them. He allowed his eyes to fall closed with the weight of his failure.
Warmth trickled over his tongue, down his throat - was he swallowing his own blood? With great effort, Severus dragged his lids open.
Again, as if conjured, a vial appeared and a thin, whiplike wand, which neatly transfered the memories from his face. He glanced up to see Hermione Granger, her face a mask of horror, tears rolling unchecked down her cheeks. For a moment his gaze felt caught on her; their eyes locked, his intense, hers stricken. Then he looked back at Potter, feeling himself weakening, his mind growing foggy, the pain too much.
"Look at me," he breathed, and Potter did.
Snape dropped back to the floor with a dull thud, his eyes rolling up, and the three friends remained motionless and silent for several beats, staring at the body of their most reviled professor.
Hermione clutched the conjured vial close to her chest; in the other, she gripped her wand so tightly that her knuckles ached. She was dimly aware that she could hear Snape's rattling breath growing shallower and shallower, and Harry's harsh breathing from beside her. Ron was backed up against the shack's wall, his face an ugly green, his eyes fixed on Snape's face in horrified fascination.
When Snape's breathing seemed to stop altogether, Harry was the first to react.
"Right," he said, still staring at their professor's body. He licked his lips. "Hermione-pass that jar here."
Hermione swallowed and gave the vial to Harry. He held it up to the dim light, frowning.
"I don't know. . . It's not. . . Did he mean these for me?"
"I think so, Harry," she said. She was shaking, she realized. "I don't know why else he'd have-grabbed you like that."
"Okay." Harry nodded and adjusted his grip on his wand. "We've got to get back to the castle then. I should have time to use Dumbledore's pensieve before. . ." He trailed off.
Ron spoke up for the first time since they had entered the shack. "Are you mental?" he demanded. "This isn't the time-!"
Harry shook his head, already moving toward the door. "I have to," he said. "They might be important." And then he was gone, his running footsteps echoing down the passageway.
Ron pressed his lips together and looked from the passage to Hermione and back again, carefully avoiding Snape's body. "Come on," he said. "We can't leave him alone."
"I-I'll be along." Hermione twisted her fingers in the strings of her magically enlarged bag.
"I've got to. . . take a minute." She made a shooing motion, her heart drumming so quickly that it was almost painful. "Please, go on, I'll catch up."
Ron looked at her for a moment, his expression, for once, unreadable, then nodded. "Be careful when you come after us," he said, then disappeared down the passage.
Hermione stared after her friend's retreating form for a moment before turning decisively and kneeling beside Snape. She bent over him, swallowing hard against the metallic stench of blood, and looked down at his face, her body completely still. Even in death, his facial muscles were tense. Even death couldn't erase the deep lines his tension cut beside his mouth and his absurd nose and between his heavy brows. Even death. . .
With a start, Hermione realized that she could hear someone breathing, just barely, and it wasn't her.
"Oh God," she whispered, momentarily frozen. Her eyes flew to the wound in Snape's neck; garishly ugly, it still oozed blood steadily.
"Bugger!" she muttered, and began rummaging through her bag. How could she have missed such as obvious sign of life? Her fingers fumbled past shrunken textbooks and changes of clothing until they curled around a small, tightly-stoppered glass beaker, a third full of a thick red liquid.
Scooting closer to her former professor, Hermione lifted his head gently, tipping it back to rest against her thighs. She pried his lips apart with trembling fingers, then yanked the stopper from the beaker with her teeth and tipped the entire contents into his mouth.
Dropping the beaker on the floor, she forced Snape's jaw shut and began massaging his throat to force him to swallow. The short dark stubble that covered his cheeks and jaw was rough against her fingers, and a bit of the blood replenishing potion had managed to dribble from the corners of his mouth before she closed it and now oozed stickily over her knuckles, but Hermione did not stop massaging until he had swallowed the rest.
Dropping her hands, she nearly moved to grab her bag again before shaking her head roughly at herself, wasting precious seconds doing things the Muggle way. Pointing her wand at the bag, she said, "Accio bezoar!", and reached up at the last second to catch the small stone as it hurtled toward her.
Wasting no more time, she shoved her wand back into her sleeve, forced Snape's mouth open once more, and shoved the bezoar as far down his throat as she could.
Nothing happened. Hermione was unsure what she had expected-nothing in particular, most likely, as she had been acting mostly on instinct, without time to formulate a hypothesis. She hadn't been present when Harry saved Ron with a bezoar last year, and at the time she hadn't thought to ask her overwrought friends what, specifically and in the proper sequence, the effects of the bezoar had been as it counteracted the poisoned mead. Please, and thank you.
As it was, Snape remained unconscious, the lines of his face still tight, whether from pain or something else she was uncertain. The wound Nagini had inflicted was still bleeding. Hermione stared at it for a moment, feeling the same odd, contrasting pulls of revulsion and curiosity that drew Muggles to slow down and stare at auto accidents, then pressed her lips together and pulled out her wand again, pressing the tip against Snape's neck. A hastily muttered healing spell and the wound had sealed itself, albeit clumsily. She gazed at the red, gnarled-looking twist of scar tissue regretfully for a moment. She had never learned healing properly; what little she did know was amateurish at best and gleaned entirely from books. She was pretty sure that particular spell was intended for lesser injuries-the cuts and scrapes that children brought home routinely-but at least there was no more blood. A scar, she told herself, was a small price to pay for Snape's life. If he did live.
She moved abruptly, shifting his head from her lap, gently, and laying it on the rough floor, which looked extremely uncomfortable. Thinking quickly, she transfigured the beaker she had discarded into a pillow, easing it under his head. Her fingers tangled briefly in his hair, which was limp and greasy as ever, and she extricated herself as gently as she could before finally standing and gazing critically at him for a moment.
He was still breathing. It would have to be enough.
On impulse she bent, reached down, and touched his shoulder with the tips of her fingers. "Please live," she whispered, trailing her fingers up over his blood-stiffened collar, bypassing the newly healed scar to brush his cheek before drawing back once more.
Ignoring the hard lump that had formed in her throat, Hermione turned and, without looking back, raced down the tunnel after her friends, toward the battle she knew was coming.