A softer hiss, more of a whooshing noise, emanated from the "back" of the capsule. Dinah’s ears felt a change in pressure, but they didn’t pop—suggesting that the pressure had just increased . She knew nothing about this capsule, but she did know how simple life support systems worked, and she knew that they would likely contain a store of compressed oxygen that would be bled in to compensate for what was being turned into CO 2 in the occupants’ bodies and absorbed by the scrubbers. The mechanism was probably trying to compensate for the air that had just been voided into space, bringing the pressure back up to normal.