No one will use this anymore...
Inspecting the stove after killing Toriel.
"Empty House" is the 16th track of the Undertale Demo OST. It plays in Toriel's Home after Toriel is killed. It is a version of "Fallen Down" slowed down to 0.4 speed and pitched up.
Despite not being in the Undertale Soundtrack, it still plays in the final game when in Toriel's Home. The first room the protagonist enters at any moment after Toriel is killed plays the song quietly. Any room following this will play the song at an even softer, barely audible volume. Falling asleep on the bed or simply turning off the lamp in the Guest Room will play the song at a normal volume. The song stops playing after turning on the lamp, and will resume playing upon exiting the Guest Room.