Yesterday whilst scrolling down your Twitter timeline, you may have seen something that resembles an ocean reef, so you probably kept scrolling. Then, a little further down, you saw the same image, only this time, you stopped and realized the picture is actually of a blood clot in the shape of a human lung.

The Atlantic reported that a man suffering from heart failure coughed up a six-inch-wide blood clot in the exact shape of the right bronchial tree of the lung it was blocking. Doctors could not believe the clot stayed intact.

The photo was released in late November as part of the New England Journal of Medicine’s Images in Clinical Medicine series. University of California at San Francisco doctors Gavitt A. Woodard and Georg M. Wieselthaler wrote that it came from their patient, a 36-year-old man who had long struggled with chronic heart failure and was admitted to the hospital’s ICU.

While in the unit, the patient suffered many episodes, including a strong bout of coughing that led him to produce the clot.

The patient was later extubated and “had no further episodes of hemoptysis,” the doctors wrote, but a week later he unfortunately “died from complications of heart failure (volume overload and poor cardiac output) despite placement of the ventricular assist device.”

After the Atlantic published the story, the image of the clot went viral.

The constant posting of the clot was enough to give some people on Twitter nightmares.