"William James describes a man who got the experience from laughing-gas; whenever he was under its influence, he knew the secret of the universe, but when he came to, he had forgotten it. At last, with immense effort, he wrote down the secret before the vision had faded. When completely recovered, he rushed to see what he had written. It was 'A smell of petroleum prevails throughout'."

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But this is touching, Severus,” said Dumbledore seriously. “Have you grown to care for the boy, after all?” “For him?” shouted Snape. “Expecto Patronum!” From the tip of his wand burst the silver doe. She landed on the office floor, bounded once across the office, and soared out of the window. Dumbledore watched her fly away, and as her silvery glow faded he turned back to Snape, and his eyes were full of tears. “After all this time?” “Always,” said Snape.

— J. K. Rowling