"What do you have in mind?" asked Jeff.
"I want it to be a surprise" said Mary. "And I want you to transform with me." Jeff agreed.
Mary took a vial from the box, keeping the label covered, and drank half. Then she poured the other half into Jeff's mouth. He thought it tasted salty, but swallowed it anyway. Mary put the vial back.
"So any hints?" asked Jeff.
"We should probably move out by the pool" suggested Mary.
Jeff quickly conclude it was some kind of fish transformation. He was glad they had a salt water pool instead of the more common chlorine pool. The couple stepped their back door onto their pool deck on this sunny afternoon. A large fence provided privacy from the neighbors.
Jeff absentmindedly rubbed his arm and found his skin felt dry and rough. Was it the beginning of his change?
"Any other hints?" asked Jeff.
"There was one kind of story in your browser history was more appealing than the rest" said Mary. "And it goes along with a little fantasy of my own that I never told you about."
Now Jeff was really intrigued. He pulled Mary in for a kiss and noticed her skin felt dry and rough like his arm. Now he knew it had to be part of the transformation. Some kind of mermaid perhaps? For some reason he found the odd skin texture attractive. Before he could say anything, Mary suddenly cried out in alarm and collapsed against him.
"I can feel the transformation starting." Her body spasmed then her shorts ripped to reveal a tail growing from her tailbone.
"What the hell?" exclaimed Mary. "That's not what I was expecting!"
Jeff looked at the gray finned appendage. "It looks like shark's tail. And that would explain our skin changes."
"Yeah, it was the shark vial. I was just expecting half the vial would be more like a shark-tailed mermaid."
Jeff felt a growing sensation in his own tailbone. He lowered Mary to the deck and pulled off his own shorts and underwear to find all the skink in his midsection and upper legs was turning gray too. He doubled over as he felt is his own tail began to grow. He pulled off his shirt as well. Meanwhile Mary managed to remove her torn shorts followed by her shirt. The gray color was spreading over her whole body.
The transformations were making Jeff aroused, which Mary noticed. She watched him change, admiring the gray and more muscular form Jeff was taking on. But she especially admired the big gray torpedo between his legs. Mary plunged into the pool and Jeff dove in after her. The couple embraced and kissed, their mouths seemingly unaffected by their changes.
"I once got really drunk while watching Shark Week and ended up masturbating to a documentary about shark mating practices" admitted Mary. "Ever since then I've had a fantasy about having sex with a shark man."