A mysterious and somewhat gross photo of a man's blood clot is getting a lot of attention after the New England Journal of Medicine shared it on Twitter.

The clot was spit up by a 36-year-old man who suffered from chronic heart failure, according to the peer-reviewed medical journal. He died not long after. What's so bizarre about the clot is it's a cast of his right bronchial tree — that doesn't really happen. It would have been more understandable if the clot came out in parts, but the fact that it came out so complete is astonishing, Georg Wieselthaler, a transplant and pulmonary surgeon at the University of California at San Francisco, told The Atlantic

"It’s a curiosity you can’t imagine — I mean, this is very, very, very rare," he told The Atlantic.

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There was a case of a 25-year-old pregnant woman who coughed up a small cast of her bronchial tree, and later went on to recover and give birth to a healthy baby, according to a 2005 report in the European Journal of Cardio-Thoracic Surgery. A 34-year-old woman was cited in 1926 as coughing up a cast of her trachea, both bronchi, and several bronchioles, according to a case study in The Journal of America Medical Association. She died a day later.

In the case of this man, he died from heart failure complications a week after doctors tried to stop bleeding and open his airways with a breathing tube. 

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