"Oh my gosh! Elsa!" said Snow as she entered their dorm room. "That's your sister! And…you're gay? What the heck? And…is that your sister?"

Panicked, Anna slammed her legs shut, clamping her thighs together. It didn't occur to her in the moment that she was trapping her sister's hand inside her pussy.

In that same instant, Elsa cursed herself. Why couldn't I take two seconds to lock the door? Why did I have to hug Anna from behind, and pull her onto my lap? Why did I have to swivel the chair so we were facing the door? (Because she didn't want to face the window, but that didn't occur to her at the time.) Why does she have to be so sexy and beautiful? And why the fuck in the first place did Anna have to tell me she wasn't wearing panties under her skirt?

Anna's eyes were wide with fear, Elsa's face blank with shock, but Snow couldn't help staring at Anna's lap, Elsa's hand half-draped by Anna's skirt. Even so, she still saw the image she glimpsed as she opened the door: the strip of red hair above Anna's pussy, two of Elsa's fingers buried inside and working steadily, Elsa's other arm around Anna's waist with her hand cupping Anna's breast, Anna gripping the arms of the office chair, her head back and eyes closed, a hot blush spreading from her cheeks down to the exposed skin above the scoop neckline of her top.

Anna was the first to break the three-way paralysis. "I swear, we were just studying biology! Yep, that's it…studying biology."

Snow's eyes darted from Elsa's face to Anna's and back again. "But…what are you doing? Biology? And isn't that your sister?"

With utter sang-froid Elsa said, "Anna, this is my roommate Snowdrop Margaret White. Snow, this is my sister Anna." Anna leaned forward and extended a hand. By force of habit Snow shook hands, even as Elsa's hands remained on Anna's breast and pussy. "And yes, before you entered without knocking, we were studying biology."

Snow, all evidence to the contrary, believed herself at least reasonably worldly. "Really? That's what you were doing?" she said, using the portion of her brain that wasn't locked in a loop of sister sister sister sister gay sister sister lesbian sister sister sister

"Of course. I'm studying the composition of female vaginal lubrication. It's really very complex, and not nearly as well understood as it should be." Snow made an eep sound as Elsa continued. "In particular, I'm interested in the function of the Skene's gland. It's homologous to the male prostate gland, and is reportedly the source of the somewhat-controversial 'female ejaculate.' Generally produced by the stimulation of the equally-controversial G-spot."

"But…your arm. Your hand," said Snow, indicating Elsa's hand cupping Anna's breast, Anna's still-erect nipples visible through the thin material of her top. "You're, um, hugging her."

"What, and risk her falling off?"

"But why is she in your lap?"

Elsa rolled her eyes. "You wouldn't want us to do this in my bed, would you? That'd be weird."

Snow took a deep breath. "But she's your sister!"

"I couldn't very well do this with a stranger, now, could I? What would you say if I asked you to provide a sample like this?"

Snow pictured herself in Elsa's lap, Elsa's left hand massaging her nipple, Elsa's right hand buried inside her. Her ass pressed into the warmth of Elsa's lap, Elsa's breasts against her back…

"I think you broke her," Anna whispered to Elsa.

"Snow. Snow!" Elsa waited for Snow's brain to reboot. "I'd like to try to get back to collecting my samples, if you don't mind." Staring defiantly at her roommate, Elsa resumed making her fingers squirm inside Anna's vagina, her other hand massaging Anna's breast, her fingers scissoring on the nipple that poked between them. She cleared her throat meaningfully, as Anna tried her very best to look professional and not moan.

Snow shook her head vigorously. "Elsa. You are doing sex things. You are having. Sex. With. Your sister. In front of me!"

"Sex? With my sister? Ew, that's sick. I don't know how you could even suggest that," said Elsa, as Anna's eyes drifted closed and her hips began to slowly rock, her breath hissing out her dilated nostrils.

"I – "

"And now, thanks to you, I don't know how long it's going to take me to do this. I might be trying to collect a sample all evening. So if you could do me a very great favour and give us some privacy? If you please?" Elsa raised a meaningful eyebrow.

"I, um, sorry." Snow left the room, closing the door behind her.

She opened the door again. "But why couldn't you use your own – "

"Comparative samples."

Snow left. After a long pause, she poked her head in. "But why couldn't she – "

"Doing. Biology," growled Anna. "Get. Out."