"Hello?"
"Hi, Mark. Please come over to my house right away. I've got something really special I want to show you."
Mary spent the next few minutes alternating between puffing herself up bigger and peeking out the window. She was having a surprisingly good time seeing her familiar surroundings from a slowly rising perspective as she swelled larger and larger. She was just considering deflating and seeing things from the other extreme when she heard a car pulling up in her driveway. Giggling, she picked up the vials and snuck into the other room, being careful not to bump her head against the doorway.
Seconds later, Mark entered, looking around for Mary. "Mary? Where are you?"
"I'm in here, Mark," Mary purred enticingly. From the tone of her voice, Mark had a feeling he was going to really like this surprise. He stepped eagerly into the next room, then froze, his jaw hanging in shock.
"Hiya, handsome," Mary said with a demure tone. She was posing sexily with the vials under one arm, her head pressed against the ceiling, and her tail swaying behind her. "Wanna have some fun?"
"M...Mary?! Wha--you--how--"
"With these," she purred, showing the box of vials to him." Every one of these vials has a formula for a different change. It's quite an experience."
"But--"
"Ssssh." Mary pressed a finger on his mouth to quiet him down. "No need to ask so many questions, handsome. You ought to try some of these..." Mary moved a hand across her figure. "...unless you'd rather try some of ME. I'd love to show you some of the things I can do in this form. I can be big and beautiful..."
With that, she pressed a finger into her navel and slowly deflated, stopping when her head was level with Mark's belt.
"...or small and CUTE!" She placed her hands behind her back, and looked up at her boyfriend, batting her eyelashes. "Mmm...you'd even more handsome from down here! How'd you like to hold this little kitty in your big, strong arms?"
Mark had to admit, Mary's offer was strangely enticing. And he was interested in what else those vials could do.