It's a common procedure in which a doctor inserts a small artificial tube into the middle ear to help drain excess fluid and keep the ear earache-free. As a result of illness or a birth defect, some people don't hear well, and some don't hear at all. If they don't hear well, sometimes hearing aides can help them hear better. People who are entirely deaf, however, have to rely on their other senses even more to provide them with information about the world around them. Most humans can distinguish over 1500 tones.
Many animals lack ears altogether.
Fish don't have ears. Over 100 decibels. Beware of sounds at the upper end of the human hearing spectrum.