Warning. The following video may disturb some viewers. It was taken in Mexico when an enormous flock of birds fell from the sky and dropped dead in the streets. It happens so suddenly, residents were shocked.
Some theories have inhaled fumes as the cause of their death, while some think it have been an overcharged power line. But some on social media say it's the type of bird.
Some theories are less scientific and come from a man who has never seen a flock of birds take a rest.