At exactly 1 hour 13 minutes and 45 seconds into the movie, Tyrone hits Harry in the RIGHT arm. Harry flinches in pain because he supposedly has an infection in that arm from shooting heroin. However, later in the scene you clearly see him shoot heroin into the wound, which is in his LEFT arm. You can first see that the wound is in his left arm 1 hour 17 minutes and 41 seconds into the film. The wound remains in his left arm throughout the remainder of the movie. This is a fairly large slipup because his infection later becomes so important and this first scene is really one of the first times you get to see how bad it has become.