What happens when millions of people in a city with poor infrastructure ceremonially sacrifice animals before a torrential monsoon downpour?

Rivers of blood flow through the city.

On Tuesday, Bangladeshis celebrated Eid al-Adha — known in South Asia as "bakri eid" or "goat eid" for the animals most commonly sacrificed as an offering to God, commemorating Abraham's willingness to sacrifice his own son. It is one of the holiest days on the Islamic calendar.

It is customary to divide the meat of the sacrificial animals equally between family, friends and the poor.

Bangladesh's capital, Dhaka, is one of the most crowded cities in the world. To avoid the chaos of so many people performing the ritual sacrifice wherever they pleased, the city's municipal corporations set aside 1,000 designated sites. They are also supposed to ensure that drainage systems along the city's roads are clear.

Reports in local media indicate that neither of those precautions were taken too seriously.

So after seasonal rains swept in, Dhaka's residents were accosted with the surreal sight of blood mixed with rain and the detritus of the city rising on its streets.

Watch a river of blood flow through Dhaka's streets (YouTube/Jaodat Rahman)

In a city used to waterlogged commutes, residents proceeded to go about their business. But for them, and for the rest of the world, the images of blood in the streets will remain unforgettable.

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