Most sea cucumber bodies are covered with tube feet, but only the ones located on the bottom of their bodies are developed enough for use. Sea cucumbers use these feet mainly to attach themselves to the bottom, rather than for motion. The tube feet are controlled by changing the water pressure of the animal. By increasing the amount of water, the feet can be extended; and by lessening the amount of water, the tube feet contract. Surrounding its mouth are 10 to 30 modified tube feet. These sweep the surrounding water, capturing bits of food, and are then transferred one by one to its mouth to wipe off the food. Sea cucumbers breathe as water is pumped through two respiratory trees located on each side of their digestive tract. Some can eject their digestive system and associated organs when disturbed and grow a new set within a few weeks.