Air Bubbles (気泡 Kihō?) are large bubbles filled with oxygen that appear in the Sonic the Hedgehog series. In underwater-themed levels they periodically rise in small clusters from cracks in the floor. These bubbles provide extra air for playable characters to breathe, and they are necessary to survive being underwater for longer periods of time. Without using air bubbles underwater, the playable character will eventually drown, thus causing the player to lose a life.