I'm still scared of the shower...
I believe that Norman bates displayed sinister nature threw his attitude, the camera angels of when he is being filmed and the lighting. Everything is put together to portray Norman bates and a very evil and sinister Character. This adds a lot of suspense to the movie.
Norman bates has a very evil attitude whenever he is alone with his mother and he thinks that it is ok because no one has told him otherwise. When his mother died he tried to keep his mother alive by being his mother. Norman bates has multiple personality disorder which tears a person in two so that is why he is very sinister because he wants to keep his mother alive ever since she passed away so he tries to be her. How