In a new study published in PLOS ONE — named, hilariously, the «pull my finger study» — the researchers slowly pull a man's fingers with a cable and used MRI video to capture (in less than 310 milliseconds) what happened inside his joints to cause
those distinctive popping sounds.
Punctuating their displays with swishing, hooting and
popping sounds, males bob their heads, fan their tail feathers, raise their wings, and expand and contract
distinctive yellow air sacs to compete for females» favor.