Hair cells play a critical role in our hearing. When they are damaged, doctors say they act like blades of grass. When someone walks on grass, the blades initially lie down and then bounce back up. but if you keep walking that same path over and over again, the grass will stay down. Hair cells are the same way, if you send waves of sound from the outside without opportunity for the cells to recover or you rip them up through excessive noise. Hair cells do not grow back.