After a few seconds, I heard someone talk from inside of the room. But I thought he was sleeping? Who is he talking to?

I leaned my head on the door to listen.

"What's wrong with you? Why don't you answer?" asked Yeol.

Huh? Who is he talking to?

"What now!?" he asked in a high voice, as if he was angry.

Seriously, is he talking to himself?