Sally decided to go to the beach for the first time since her treatment. In the past she had enjoyed laying on the beach, soaking up the rays and working on her tan. Today she took one look at the gentle waves lapping against the sand and thought about throwing her things down and running right into the water. Shaking her head at the urge, she spread her towel and lay down on her back. Sally found this strangely uncomfortable and her skin felt dry too.
She sat up and stared at the water again. She decided to heed the ocean's call. She waded out until it was waist deep then dove in. The salt water felt so good! She swam out just beyond the faint line of breakers then turned parallel to the beach. Her skin felt better than it had in weeks, but her back was itching like crazy. Sally tried to ignore it. Finally her upper back spasmed and the itching stopped. She continued to swim and when she stopped for a breather she heard screaming. Looking around she couldn't see anyone in distress but she could see people making their way out of the water. Then she heard a shout of "Shark!" Sally turned back to the beach, swimming as fast as she could. She didn't think the injection of shark DNA would do anything to keep sharks away from her.
As she waded out of the water onto the beach, Sally noticed people staring at her with a variety of expressions. An attractive lifeguard approached her with a towel.
"You seem to have lost something while you were swimming" he said and offered her the towel.
Sally looked down and was surprised to find her bikini top was indeed missing. She took the towel and covered herself up.
"Thank you" she said.
"It's not very inappropriate of you to wear a shark fin on your back and scare all the people on the beach here."
"What are you talking about?" Sally asked with complete sincerity.
The lifeguard reached behind her and grabbed something which he gave a slight tug. Sally felt it.
"What are you doing?"
The lifeguard gave another tug, which Sally also felt. It was like someone pulling on her arm, except she didn't have an arm on her back.
"I know this is going to sound strange, but you have a dorsal fin."
"What?!"
Sally heard a snap of a nearby smartphone. She turned to find another young woman with her smartphone who showed her the photo. Sure enough there was a dorsal fin on Sally's spine right between her shoulder blades. Although the fin was the same color as her skin, it otherwise looked very much like a shark fin. Sally suddenly understood why her back was bothering her and had a guess why her top had fallen off.