Su Er ended his Animagus Transformation, returning to his original appearance before Hermione's eyes.
"When did you find out?"
Hermione answered him with a huff, her expression saying that it was just as she had thought.
"I knew I'd given myself away..." Su Er muttered with an awkward smile.
"Hmph." Hermione folded her arms, and a flush crossed her face at some unspoken thought.
Only after a long while did she part her soft pink lips. "Hey, how did you avoid being detected by the girls' dormitory's magic?"
"I don't know either... Maybe it's something special about this magic." Su Er glanced cautiously at Hermione and shook his head. "I'm more curious about when you figured it out."
At that, Hermione looked pleased with herself.
"I sneaked into the Hospital Wing," she said. "The moment I saw that you in the hospital bed, I knew something was wrong."
"What was wrong?"
"The posture, the expression," Hermione said with certainty. "They weren't the same as I remembered."
Were they? Su Er scratched his head. He had watched Professor Dumbledore turn one of Fawkes's feathers into him with his own eyes. At the time, he had been astonished by Dumbledore's Transfiguration, which defied the laws of the subject.
"There are always more solutions than problems, aren't there?" That had been Dumbledore's answer.
"Since the one in bed wasn't you, wasn't it obvious where you might be?"
Once Hermione started talking, she could not stop. She paused and gave Su Er a sidelong glance.
"Since you couldn't appear in the Castle, there was only one way: turn into something else or leave. Or else stay here in the Room of Requirement, where you'd be completely safe and no one would discover you."
"Besides, I noticed that you and your transformed self could never