From inside the room, Chara reaches the door just as Tauriel starts to bolt down the stairs. They can hear Tauriel speaking- and they wonder what hên vell means, though it's obviously an endearment of some sort- and then that other voice.

It's Frisk. But Chara can't quite make out what they're saying, the other child's voice is so soft and hoarse. So Chara carefully lies onto the floor and presses their ear against the bottom of the door, hoping it'll help. Somehow.