Because the brain stem is what transfers all information to the rest of your body. Also, it is directly connected to the hypothalamus, which if damaged, can take away your ability to breathe or do simple tasks.
War and hunger hahha funny cuz im writing a book like that
Feel better and develop communication skills
Well it should show drugs that are in your systems, I suppose it depends on how long you think the drugs have been in your system and the home drug test you choose