Leonard Shelby: I have to believe in a world outside my own mind. I have to believe that my actions still have meaning, even if I can't remember them. I have to believe that when my eyes are closed, the world's still there. Do I believe the world's still there? Is it still out there?. Yeah. We all need mirrors to remind ourselves who we are. I'm no different.
In the scene in which Leonard writes on the back of his picture of Teddy, "He is the one. Kill him," we see a shot of Leonard placing the picture on top of his tan jacket on the bed as he goes to write on it. Then, it goes to a close-up of the picture in which the jacket has disappeared and the picture is lying directly on the blue bedspread. It actually happens twice within that same scene.
In the scene where Lenny is on the phone describing how Sammy Jenkis ends up in a home due to the death of his wife, it shows Sammy sitting in a chair looking towards the camera. Sammy is temporarily blocked from our view by someone walking in front of him. As the person passes by, it is not Sammy that re-appears, but Lenny. To see it well, you will have to use the frame-by-frame mode. There are about 5 visible frames of Lenny in the home, and then it cuts back to him inside the motel room talking on the phone again.