In the second phase of testing, called "Pressure Testing", candidates who have successfully performed the Valsalva maneuver will be subjected to increased ambient pressure. This test is performed under the supervision of a diving-certified medical doctor. All testees enter a pressure chamber, accompanied by the doctor, and the 'tank' is sealed. Typically, there is in the chamber a somewhat surprising object: an inflated volleyball, water polo ball or similar inflated ball. Upon sealing the tank, pressure is increased, while the testees equalise their eardrum pressure. (if any testee is unable to 'Valsalva', the test stops, and pressure is slowly released.) Pressure builds within the chamber until the chamber is equal to water pressure at "escape depth". At this point, the chamber feels very warm and dry, and the volleyball has become compressed enough that it has become the shape of a bowl, and appears to have been emptied of air, due to the greatly increased air pressure inside of the tank. Sounds inside the tank at pressure sound as if they are "far away".