A tennis ball has rolled its way down into a hole. This particular hole is extremely deep and has a sharp bend in the middle, making the ball impossible to retrieve by hand. The ground around the hole is made of hard clay, so digging the ball out isn't an option. What could you use to get the ball out?
Water. Pour water in the hole and it will float to the top for you to get.
What never gets any wetter no matter how hard it rains?