Jon Gosselin knew something was seriously off when grueling pain started in his leg and eventually spread to his upper shoulder. “I coughed up what looked like silly putty – it was a blood clot.”What Jon did next? Deep-vein thrombosis, or DVT, occurs when blood clots form in the deep veins of the body, typically in the legs. It’s a drug that prevents blood clots,” he explained. They scanned my whole body for blood clots,” he said.