Missy looked out the window. "Meemaw's finally gone. As long as nothing else happens, we can finally show everyone how adult we are!" Sheldon glared at her due to her bad grammar. "You mean "how mature we are". Besides, even if everything else goes right, only one of us fits that description." "Really?" said Missy. "Yes." retorted Sheldon. Missy stared at him, peeved. Then she remembered something. Smiling, she said, "I know something only adults know." Sheldon scoffed. "I doubt it." Feeling confident, Missy walked towards Sheldon, the distance between them quickly becoming uncomfortable for him. She leaned towards her brother's ear and whispered, "I know how babies are made." Shocked, Sheldon pushed away from his sister, trying to gain some distance. "How do you know that?" Sheldon exclaimed. Missy smirked. "I have my ways." Sheldon was unsure if Missy was telling the truth, but he had to know, for the sake of remaining smarter than her. "Fine, if you know, then tell me." "Okay.", said Missy, "Let's talk in our room, in case anybody else wants to peek in on us; no one can know I told you this." Missy led Sheldon to their room, and closed the door.

Missy pointed to Sheldon's bed, where he sat down, and Missy followed. "So, how is it done?" asked Sheldon. Missy thought for a moment, trying to recollect exactly what she learned. "To make a baby, a boy has to put his thing in a girl's." Sheldon was confused, so he asked, "Girl's thing? I remember that, when we used to bathe together, you clearly didn't have one. By the way, a boy's "thing" is called a penis, I looked that up myself." Missy was annoyed by his correction, but kept going. "A girl has a hole between her legs that the boy puts his, I guess penis, in." "I believe that's your anus, or butt hole, for the lay person, and, we all have one." Missy was getting fed up with all of Sheldon's doubt, so she took drastic measures; "Fine, if you won't believe me, then I'll just have to show you."

"Hey! What are you doing?" Sheldon said, as his sister stood up, and began to strip right in front of him. She began by kicking off her shoes and pulling down her purple pants, revealing her panties underneath. Next, she pulled off her flower covered turtleneck, revealing her flat chest. After calming her nerves, she sat back down onto the bed. Sheldon was, once again, shocked by his sister's actions. But, this time, the shock was more positive. "It's been a while since I've seen you with so little clothing, but you seem to be filling out nicely." Missy was surprised by the comment, not really knowing how to react. "Thank you?" she said, "Anyway, let's continue." Sheldon nodded. Missy laid back onto Sheldon's pillows, and grabbed the waist band of her panties, but stopped, thinking. "Sheldon", she said, "could you take your clothes off too?" "Why?" asked Sheldon. Missy wanted to get something for herself out of this lesson, but she had to word it carefully, otherwise, Sheldon would never bite. "Call it an EXPERIMENT."

Hearing that word, he decided to, hesitantly, go along with her plan. Missy Cooper might not have had her brother's IQ, but she was clever beyond her years. Sheldon scooted off the bed, stood up, and began to strip, starting by untying and removing his shoes. He worked his way up; unbuckling his tan pants and pulling them off. Lastly, he unbuttoned his plaid shirt and pulled that off as well. Once he was standing in only his briefs, he turned towards Missy, who was blushing a little. "Alright", said Sheldon, "what's the experiment?" "Right.", said Missy. "Clearly, I don't know how to explain how babies are made with my words. So, my idea is that we try it out ourselves." Sheldon really didn't know how to feel about this, but, for the sake of science, he had to go through with it. "Fine, but I have a few questions first." Missy was tired of waiting, but figured she had to go through this to get to the good stuff. She sighed, "Shoot." "Alright.", Sheldon said, "First, does it hurt?" "No, the exact opposite." Missy responded, "If it hurt, people would never have children again." "Fair point." Sheldon noted. "Second, if we do this, won't we make a baby?" "No, people can't actually make a baby until they're physically adults." Sheldon was relieved, "Okay, that was the last of my questions." Missy sighed in relief, "Finally. Now climb on up here."

Sheldon climbed onto the bed and sat down, sitting on his feet. Missy grabbed the waist band of her panties again, this time pulling them all the way down to her ankles, and off completely. "Wow.", exclaimed Sheldon, staring at his twin's crotch. Missy noticed Sheldon gaping at her naked body, and decided to snap him back, "Sheldon! Your turn!" "Right!" confirmed Sheldon. He sat back onto his butt and wiggled his briefs out from under himself, down to his ankles, and off. He kneeled and started walking on his knees over to Missy. This time, she gaped at Sheldon's naked body, starting from his chest, down to his penis, which was erect and pointing directly at her. "Awesome", she said. "So what do we do?" said Sheldon, bringing Missy's gaze back up to his eyes. "Uh, right, so..." Her face was bright red. "You have to..." She slowly spread her legs.

"Put your penis in the hole in my crotch." "Where is the hole?" Sheldon asked. "You have to find it between my folds." Missy said, schemingly. "Alright.", Sheldon said, as he bent down onto his hands and knees. He began to inspect Missy's crotch by looking all around it, smelling its intoxicating scent, and, finally, taking his right hand and spreading her folds. A shiver went up Missy's spine as she bit her bottom lip, trying not to get too excited yet. With Missy's folds open, Sheldon could see a hole that looked about right, but also another, smaller, hole. Sheldon asked, "Which hole is it?" Bringing her thoughts back into focus, she answered, "The middle one." "Then what's the smaller one for?" he pondered, poking it a little." Missy began to get more excited, but managed to answer, "That's where my pee comes from." Nodding his head in understanding, Sheldon poked the other hole, putting his finger in a little. This caused Missy to gasp, saying, "Let's get going already." "Okay.", Sheldon said, "I just wanted to make sure I understood everything first."

Missy calmed down a little as Sheldon got up from his hands back onto only his knees. His penis was throbbing from looking at Missy's crotch so much, and Missy was getting very wet from all of Sheldon's touching. Sheldon inched a little closer to Missy and prepared for further instructions. Missy saw he was ready and said, "Now, slowly slide your penis into me." Sheldon lined up his penis and put its head to her opening. Missy gasped louder this time, loud enough for Sheldon to take notice. "Should I keep going?" he asked. "Hell yes!" Missy exclaimed. Sheldon was caught off guard by her language, but got the message. He slowly slid his penis into her hole, causing her to open her mouth, as if trying to gasp, but no sound came out. Once he was in all the way, she inhaled and exhaled slowly, and then gave the next order, "Now, slide your penis back out until only the head, the fat part at the end, is still in me." He did so, causing the same reaction from Missy. "Now, keep doing that for a bit." Sheldon began pushing his penis into his sister, and then pulling it back out of her, slowly, while taking note of every bit of the experience. She was extremely tight, most likely due to her age; she was very wet, which helped with the insertion; and her hole was so soft and warm, almost hot, which made him want to never pull out.

As he continued he felt her twitch and clench around his penis, as well get a little restless on the outside. "Sheldon, could you start going a little faster?", Missy began to grumble. Sheldon sped up a little, but Missy was not satisfied. "Oh, let me show you." She grabbed her brother around the neck and flipped them both over, so that she was now on top of him. "Here we go." Missy said, pinning Sheldon to the bed, his penis still in her. "Just let me do the work for now." she insisted, "I can keep this at my own pace that way." "Fine.", Sheldon said, knowing he could never win a wrestling match or argument of wits against her. "Let's see here." Missy placed her hands on Sheldon's abdomen, trying to get into a comfortable position. Once she got a good grip on Sheldon, as to not fall over once they continued, Missy began to move her hips up and down, slowly, getting back into the rhythm of what they had going. However, now that she was in control, she decided to take it up a notch.

Missy lowered her hips all the back down, so Sheldon was all the way inside her. Then, she slowly brought her hips back up, as to pull out everything but the head. After she prepared herself, she slammed herself back onto Sheldon's penis, shocking both of them with pure bliss. "Keep doing that." Sheldon ordered. "With pleasure." Missy responded. Over and over, Missy picked up her hips and then slammed them back down onto Sheldon. After a little bit, she got the rhythm back to the point she didn't even have to think about it, her body was just having sex automatically. Sheldon could not believe what he was feeling, thinking, and in this moment, doing. He reached out, as if being controlled, and put his hands on his sister's butt cheeks. Missy was moaning and gasping for air, completely enveloped in the feeling. However, Sheldon's delicate hands were enough to break her out of her trance for a second. "Why are you touching my ass?" asked Missy, between breaths. "I don't know." gasped Sheldon, "It just felt right." "Fair enough." And that was all she said before kissing Sheldon right on the lips while continuing her humping.

She pulled away from the kiss, feeling something building up in her. "Sheldon! I'm cumming!" she yelled. "Cumming?" Sheldon asked. She didn't have time to answer before she squirted all over Sheldon, and Sheldon came all over the inside of her. "That's what cumming is.", Missy told him, falling onto his chest. "Ah..." he said, trying to catch his breath. "I want to stay in you forever." Sheldon admitted. "Well, I would love to lay here forever too, but I have to clean the mess you made inside me." Missy pulled Sheldon's penis out of her, dripping both of their cum onto his crotch and sheets. As Missy walked, butt naked, cum dripping out of her, down her leg, towards to bathroom, Sheldon said, "Maybe you are more mature than I thought." Missy looked back at him, smiling. Sheldon took one last look at her butt, and decided to clean up as well.