Bats roost hanging upside down in high places. Unlike airplanes, they do not need a runway for takeoff, and do not need to expend much energy to get airborne. All they have to do is relax their feet, drop, and they are in the air--most economical.
蝙蝠倒掛高處棲息，使它們不像飛機需要跑道助飛，也不需要大力抖翼才能騰空而起；只要鬆腳、落下，就身在空中了，十分省力。