You return from a short trip, and a backpack, of course, on your back. Opening the door, you walk inside your mother's house, Toriel. After walking in, you close the door behind you, then hearing Toriel set up a dish in the dinner table.

'Huh, must be busy...' you think to yourself and turn to your room, and entering it.

...

As you were setting your backpack down, you hear a knock at your door. Seems like Toriel was done with whatever. So you walk up to the door and open it, seeing Toriel.

She greets you with a silent wave and a cheerful expression.