you start off with a structure the bones and the bones are covered by flesh and flesh is covered with hair and freckles and things like ears and eyes and a mouth for hearing seeing and breathing
and then you get into deeper things like the lungs and heart and various organs and the brain somehow controls all of this
every thought you've ever thought every dream you've dreamt it's all happened inside of an ***** no larger than your two fists put together so when they say that it's all in your head they're telling the truth