diaphragm

The part of the human body that tightens and moves down to create lower air pressure in the lungs than in the outside environment, allowing air to move into the lungs. This part then relaxes and moves back up, generating higher air pressure in the lungs than the outside environment, forcing carbon dioxide out of the lungs. This part also separates the chest cavity (cardiovasuclar and respiratory) from the abdominal cavity (digestive system), which is why your chest expands as you breathe. Also that fancy part of an air horn that rapidly vibrates in response to air movement, generating that screeching sound.