There was clearly an easier, safer, more reliable method. Why choose the harder one?
Something had to be wrong here!
Just as this occurred to him, Edward was startled: since he did not know when his past self would emerge from the mirror, he had been carrying the Mirror of Erised around with him these past few days. That seemed rather dangerous.
Nicolas Flamel began coughing repeatedly, and Dumbledore hurriedly brought him a glass of water. "Rest for a while, Nicolas."
"Thank you."
Holding the glass in his trembling hands, he took a small sip. "That is all I know about the Mirror of Erised. In fact, after returning it to Hogwarts, I tried following the traces Slytherin had left to investigate it further. Unfortunately, I found nothing, because after returning the Mirror of Erised, Slytherin seemed to vanish into thin air."
"All right, old friend."
Dumbledore said gently, "I'll take you to rest now. Once Harry returns, we'll still have to trouble you to examine him."
"No problem." Nicolas Flamel sighed. "Ultimately, both the Philosopher's Stone and the Mirror of Erised became involved because of me. This is what I ought to do."
A few minutes later, Dumbledore returned to the office after settling Nicolas Flamel in. "What do you think?"
Audrey spoke first. "Could Slytherin's disappearance have been because... he entered the world inside the Mirror of Erised?"
The others nodded in agreement.
"But if he was so afraid of the Mirror of Erised, why would he choose to enter it?"
Grindelwald glanced at Edward and smiled. "Could he perhaps have been forced inside?"
Audrey blinked and stared at Grindelwald. "Mr. Grindelwald, were you hinting at something else just now?"
Grindelwald: "..."
Wasn't this little girl a bit too perceptive?
Edward hurriedly interjected, "Based on what we know