The discovery was made by Lance McDonald, a video game hacker and modder. By modifying the game, they managed to force the game camera in one place while the player continues forward. This revealed a terrifying secret to the game: The haunting ghost of Lisa is right behind the player, following them throughout nearly all of the game.
"She actually attaches to the player's back as soon as you get the flashlight, here, I demonstrate how you can see some strange shadows. I then lock the camera in place and walk forward, showing how she's always there... following you..."
P.T. continues to be THE horror game that got away. Originally, it was a playable teaser (PT) for an upcoming Silent Hills game, directed by Hideo Kojima and film director Guillermo Del Toro. It was even discovered that acclaimed horror manga artist Junji Ito was approached to help design monsters for the game. Unfortunately, Hideo had a falling out with publisher Konami, who canceled the game and went through every effort they can to remove the playable teaser from existing consoles.
We may never get the PT we once saw. But at least we have Death Stranding coming up.
If you're interested in McDonald's work, they currently have a Patreon to support their video content.