When I first started the demo, the first thing I tried to do was play the piano. The piano lid closes and you cannot play it. At first I thought this was just a scare, but then I got thinking about Moonlight Sonata. Resident Evil famously plays Moonlight Sonata when you interact with pianos. It occurred to me that maybe the piano was the last step - the goal is to do everything else correctly, then try to play the piano. If you have done it correctly, you will actually play the piano.
While I have seen this idea come up a few times, it doesn't seem to be the basis of very much testing. If the piano is the last step, then what is the correct sequence?
People have pointed out that there are distinct numbers written or marked on various items and objects in the house. There are some photos in this imgur album, but it's not 100% correct:
http://m.imgur.com/a/qvNqz
So let's look at what is correct.
1. There is a 1 written on the box under the TV.
2. There is a 2 on the nail of the dummy finger.
3. There is a 3 on the door of the chained armoire.
4. The "u" in the revised note after the tape is a 4, but the axe also has a 4 on it.
5. Unknown
6. The bloody handle of the scissors in the finger drawer DOES look like a 6.
7. In the comments of a thread on Reddit, somebody says there is a "big 7" above the piano. But my girlfriend is currently asleep on me and I can't reach the controller to check for myself.
But if there IS a 7 above the piano, this helps my theory that playing the piano is the final step. These other numbers must indicate some kind of sequence, meaning we have to find #5 and possibly #6, figure out how to "use" them, then play the piano...
I vaguely remember a 6 on the VHS tape, but I could be misremembering. If there is a 6 on the tape, that would be more conclusive than the bloody scissors.
Plus there are sevens everywhere. Seven voodoo dolls, seven appearances of the ghost girl, "go tell aunt Rhody that everybody's (dead)" is seven words, with the final word missing, possibly indicating the nature of the seven-step puzzle.