Your Hair and Nails Don't Keep Growing After You Die
When the human body ceases to function, all of its former duties halt. That includes the growth of hair and fingernails. What people were actually reporting on was the fact that human skin shrinks after a person dies, so their hair and nails look longer than they did when that person was alive.
Humans Can Grow New Brain Cells
You are not born with a finite number of brain cells. Your brain does not stop producing cells when you turn 25. Your brain will continue to produce more cells as your neural pathways morph and change throughout your life.