suddenly, becoming aware of himself, he noticed his trunks were gone.
Refocusing his attention on his feet, he found that he could not longer reach them, his legs were now considerably longer. The feet themselves were not webbed anymore, the smallest, outward toes were now the longest, and stretched the membrane between them and the other toes further. While he watched, individual toes faded away, leaving only the webbing surrounded on the outer parts by flesh.
Trying to move, he noticed the joints of his knees were no longer definite, and bent in any direction he chose. The separation between his legs continued to close like a zipper and merge into a single column.
his hair turned from brown to seaweed green.
Hundreds of goose bumps bulged on the skin of his legs, flattened, and pressed together, forming rough ridges. The scales mostly retained the old skin color, though they were tinted slightly blue.
He managed to lift his waist up, to inspect his recent changes under the light of the sun. For the first time he saw his modified legs all at once. For the first time it shocked him to discover that they were a fish's tail.
After a quick inspection he found that the upper portion of his body was unchanged.
"I'm a merman!" William said.
Intuitively this led him and the family to look at his midsection to discover exactly where man met fish. The transition was surprisingly difficult to find, it was gradiated between several inches. In fact, William couldn't view and recognize both sides at the same time, it was too much of a blur. What were scales on one side slowly became the goose bumps he saw earlier, then a few freckles on human skin.
His tail flopped flat, and he found his tail was nearly six feet long. In every motion, its heavy mass was revealed. Only in water could he move usefully.
he saw his bare chest as it blended into the tail. He seemed like a single unit, there was no longer any distinction in his eyes. The tail was a part of his torso and his torso was a part of his tail.