On this page of Heavy Rain's game guide you will find a description of The Lizard scene. Playing as Ethan, you must proceed to the next challenge prepared by the kidnapper. This time the hero will be faced with the difficult choice of sacrificing himself to save his son.
Important: It is one of the most moving and drastic scenes in the game. This is Ethan's third trial. There are two trophies to unlock during this scene, and they are mutually exclusive depending on which self-inflicted tool you decide to use: if you pick saw/scissors for cutting the finger, you will receive the Butcher trophy. The second trophy, Gold Finger, will be given to you if you use the knife/pincers and you disinfect or burn the wound. In addition, if you pass all five attempts (challenges) correctly, you will receive a Trial Master trophy.
You will spot porcelain lizards on the floor. There's a key in the second (green) one - use it to open the door. Listen to what this talking device has to say. Well, it's up to you. You can leave or decide to stay and cut your finger. If you choose to leave the location prematurely or do not cut off your finger within the set time, you will fail this attempt. Then, the chance of getting any of your achievements will be lost.
In case you decide to cut, the developers prepared a lot of options for you. You can use as follows: a knife in the wall in the kitchen, scissors inside the sink in bathroom, pliers next to TV...
... a saw or an axe lying on the floor. Put all of these on the table. Aside from that you must find a steel rod on the floor and you must heat it over the cooker until it's red. You will find disinfectant inside the closet in the bathroom and a flask in the kitchen, as well as small piece of wood by the window. Put all that on the table too.
Put the small piece of wood between your teeth. You can drink from a flask, it will make cutting easier. Now choose the tool you want to use to injure yourself with. To cut your finger, you will have to calm down by breathing deeply (listen to Ethan's breath, breathe deeply until he calms down). Now cut. Once you're done and Ethan get's out of shock, disinfect the wound with disinfectant or cauterize it with the rod.
You don't need to complete all actions described above - you can also select any tool you want, calm your breath and cut. It won't affect the ending of the scene, only how drastic the scene will be and type of unlocked trophies.