Sean's dick snaked down from his pants (which were really now shorts), reaching almost to his right knee. It began to swell as it lengthened. Pushing and throbbing against his already tight pants, when suddenly, they tore. The fell at least six feet to the floor. His dick hung out for everyone in the class to see. It began to throb and pulse, getting bigger and thicker with every pulse. Sean had an urge to rub it, something that he had never done before. He began to jerk off.
His balls were swelling too. Already the size of oranges, they got bigger, and bigger, untill they were each as big as a normal person's head, and they hung down at least a foot. The whole thing was very heavy.