We have a 'diving reflex', like other marine mammals. This means that special nerve endings on our faces, around the mouth and nose, trigger this reflex only when the facial region goes under water. If we are in the water, with our head out in the air, there is no diving reflex. But if we sink just our face in a bowl of water, while the whole of the rest of our body is in the dry air, the diving reflex is triggered. It automatically closes down the airway, reducing the risk of swallowing water, and it narrows the small air-passages in the lungs. At the same time the heart rate is slowed down to half speed and blood is shunted to the vital organs, protecting them from the effects of the brief stop in breathing. By contrast, if a chimpanzee or a gorilla found itself in water with its face below the surface, it would panic, its heart would race and it would quickly drown.