All eggs in a nest hatch at the same time, and the entire brood leaves the nest at once. Crocodilians' senses of smell, sight, and hearing are well developed. Their ears are covered by flaps which close to prevent water from entering them. They have vertical, cat-like pupils which dilate to allow them to see well in the dark. Crocodilians do not see well underwater.
Crocodilians have an elongate open-ear canal.
Their thoracic and abdominal cavities are separated by a muscular diaphragm, used in breathing. This allows crocodilians to breathe when their entire body except their nostrils are submerged, and also when holding prey. Crocodilians' hearts have four chambers like mammals and birds, but there is a pore between the left and right ventricles which allows some mixing. Opening their mouths can also cool them off, since the large exposed wet surface allows much evaporation. Tropical species may avoid the hot sun by remaining under water or mud during the day.