A common trick preformed by several primates, birds, lizards, insects weight lifters and porn stars as a mating ritual or to fend off any potential assailants. It's easy, try it your self. Just suck in and hold for as long as you can (Ladies make sure to maintain good posture to convey strength and a nice set of boobs), or just expand your decorative tail feathers. Now go take a walk outside and watch the members of your pride / brood /hive / office group take notice!