[Only now does Chara show an emotional reaction to this. Irritation.]

Use your head, Frisk. [They grab hold of Frisk's wrist and yank them back to face them.] Why would there be a populated house in the middle of a crypt? Why would there be people living there? How would a fire start down here naturally? How would they survive these conditions?

It's a trick, Frisk. Snap out of it!