Peacocks' special feather structure creates trippy, hypnotizing 'dance'

Peacocks, perhaps nature's most trippy bird, shake their tail feathers when it's time to attract a new mate. Why? Shaking those feathers -- called "train-rattling" -- causes an illusion where the eye-like circles on the feathers become more prominent, seemingly floating outward and hanging in the air. Those circles exist to lure in peahens, but have fascinated more than a …