From the Intrusive Thoughts Wikipedia Page:
Many people experience the type of negative and uncomfortable thoughts that people with more intrusive thoughts experience, but most people can dismiss these thoughts.[7] For most people, intrusive thoughts are a "fleeting annoyance".[8] Psychologist Stanley Rachman presented a questionnaire to healthy college students and found that virtually all said they had these thoughts from time to time, including thoughts of sexual violence, sexual punishment, "unnatural" sex acts, painful sexual practices, blasphemous or obscene images, thoughts of harming elderly people or someone close to them, violence against animals or towards children, and impulsive or abusive outbursts or utterances.[9] Such thoughts are universal among humans, and have "almost certainly always been a part of the human condition".
False. If the flesh covering the skull has decayed there's a good chance the brain tissue has also decomposed or been eaten by insects.
Also it's called craniotomy or possibly osteotomy not an "incision".