You push the blade through the slit, and hear something mechanical click from within the wall. The wall recedes into the house! You try to pull your knife out, but as the wall nearly finishes its course, you have to give up to save your hands. Bye knife.

The night is calm and soundless, with just a faint fall breeze. As you look around the area behind the former wall, you see it's filled with graves! Yet, somehow, it feels inviting, like chill wind after a hot day. You look around, and examine the retracted wall: nothing's around you, and it doesn't budge.

You cautiously enter the graveyard. It feels like it must have been a beautiful courtyard at one time, before all the tombstones. Memories of spring flowers and soft lazy days come flooding into your mind, as if hearing stories directly from another's thoughts. As you meander to the far side of the courtyard, you feel as if someone friendly were calling out to you in play, and as you turn to see them-

The way out has disappeared. All the thoughts cease. The air is cold and hollow. It's dark and you're alone.
You search for an exit, but can't break the fence open, and can't move the wall back into the house. You're stuck.

Well, all you can do is examine the graves...