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Tonight was one of those rare nights that Toriel and Sans could spend alone. Frisk was in bed, Toriel had finished grading assignments, and Sans had returned from wherever he disappeared to during the day. She was knitting in bed when Sans joined her, sneaking into the room so that she was caught off guard when he suddenly got into bed with her.
“Evening, babe,” Sans said, slipping under the covers beside her.
“Sans! I didn't hear you coming,” Toriel scolded, though her eyes were wide with delight. Toriel put down her knitting and took his bony hand in hers, leaning in to give him a kiss on the cheek. Sans returned her affection, pressing a boney kiss to her lips and stroking the fur of her paw.
“I missed you,” Toriel murmured in an affectionate airy voice as their lips parted.
“Oh? Who is this Yu? You're not seeing anyone else are you, Tori?”
Toriel burst into a fit of laughter. “And what if I am?” she teased, fluttering her eyelids at him.
“They're probably gonna have a bad time,” Sans admitted, giving her a wink.
Toriel pressed her hands to either side of her face, imitating shock. “Sans, are you flirting with me?”
“Well, you are my wife so that's definitely a distinct possibility.”
Toriel laughed softly. “Hey Sans...”
“Hmm?”
“Knock knock.”
Sans grin seemed to get wider, though he was always grinning so it was hard to really tell. “Whose there?” he responded.
“Goat.”
“Goat who?”
“Go to bed,” she said, unable to hold back another burst of laughter.
Sans laughed softly too and, despite her joke, they didn't go to bed. They spent another good hour telling each other the most ridiculous jokes they could come up with.
“Knock knock,” Sans started during another one of his turns.
“Whose there?” Toriel answered. She was visibly sleepy by this point.
“Bear.”
“Bear who?”
“My children.”
Toriel started laughing but quickly stopped, the implications of what he was asking sinking in. She pressing her hand to her mouth, blushing brightly. “Are you being serious?” she asked, the outer corners of her eyes crinkling downward. Sans had a habit of asking serious questions through jokes. That was how he'd proposed to her.
“Would that make you happy?” he asked, taking her paws in his hands again, holding them both firmly.
Toriel was caught off guard by the intensity of his stare. “Sans...” she said. “I'm old. I've already had children and...well...” her gaze fell to the bed.
“I see,” Sans said. There was a melancholy in his voice that was quite unlike him. She looked up. He was still smiling but his eyes had a hollow look to them.
“Sans...” she said, patting his head. “Even if we are biologically compatible, which we may not be, how would we even conceive?”
“The usual way,” Sans said, closing his eyes and waving his hand.
Toriel stared at him. The topic of sex had never come up in their relationship before. It hadn't seemed all that pertinent. Sans had never shown any interest in bedding her and she hadn't been particularly interested in bedding him either. “Sans...do you...do you even have the equipment?” Toriel asked, the corners of her lips dipping downward. Now that she thought about it, she hadn't actually seen him without his pants.
“Equipment?” Sans asked, looking confused.
“Genitalia,” Toriel said, looking somewhat bashful. “Do you have genitalia?”
“You mean that stuff that shoots DNA?” Sans said. “No. That's gross.”
Toriel was genuinely puzzled by his answer. “Well sort of? We're monsters so there's no DNA involved but..” She trailed off, wondering if Sans had been watching human nature documentaries. “Sans...you know that some monsters have that as part of their anatomy, right?”
Sans must have realized his mistake for he scrambled for an apology. “Well it...uh...it probably looks great on you, Tori,” he said, scratching his head.
Toriel sighed. “Can I see your body?” she suddenly asked.
“Hmm?”
“Will you undress for me?” she asked again, looking a bit bashful. “I'd like to know more about your anatomy.”
Sans gave her a thumbs up, his grin looking wider.“Sure thing, babe.”
When she saw his smile, she couldn't help but smile back. He always seemed to have that effect on her. He stripped out of his clothes, pulling off his jacket, shirt, and pants with ease. Once he got it all off he reclined back on his side, his elbow resting on the bed. Toriel almost laughed at the position. He looked like some sort of macabre painting of a french girl.
As she set to examine him, she saw about what she had expected. He had a spine, a rib cage, the pelvis, tibia, femur, and all the other bones that constituted the makeup of a skeleton. She gently ran her fingers down his rib cage and Sans giggled.
“Hey, that tickles,” he said. “You must have found my funny bone.”
Toriel chuckled. “I've always been curious...” she admitted. “You can feel things but you have no skin. What about heat and cold? Are you sensitive to that?”
“Not as sensitive as most monsters,” Sans said. “But I definitely feel your warmth, babe.”
“I guess that's why Papyrus dresses the way he does,” Toriel mused. His clothes had never seemed appropriate for...well...a snowy climate.
“Papyrus dresses the way he does because he's Papyrus.”
Toriel laughed in agreement, her gaze wandering down his spine to his pelvic bone. Like Sans had assured her, there was no reproductive anatomy of which to speak.
“Want to hear something humorous, babe?” Sans said, giving her a seductive wink.
“Is this going to be a joke about your humerus?” Toriel asked, rolling her eyes playfully.
Sans didn't hesitate for a second as he sat up and put his hand under his armpit. Despite his lack of skin, he still managed to make a farting sound by moving his humerus against his scapula. Toriel's lips cracked into a grin.
“You're making it hard for me to concentrate,” she told him, swatting lightly at him.
“Sorry,” Sans apologized, leaning in a little.
Toriel smiled and started tracing the left side of his pelvis. “So Sans...” she said, her eyes lidded, “How exactly do skeletons reproduce?”
Before Sans could answer, the door swung open. “Mom I-” Frisk started then stopped, looking through squinted eyes at the scene before them.
“Hey kiddo~” Sans greeted cheerfully. Toriel felt her face heat up like an iron cast stove. Her hand froze where it was, her finger still on the outer shell of San's pelvis.
Frisk stared silently at them for few brief seconds before taking several steps back and slamming the door shut.