Answer:
Two people are born at the same moment, but they don't have the same birthdays. How could this be?
Kills the bad ones and the sad ones. Tightens to fit, so one size fits.
When I live I cry, If you don't kill me I'll die.
What is eaten but not grown and was born in water but will disappear if soaked?
This is needed both for courage and hardcover books.
You use it between your head and your toes, the more it works the thinner it grows.