Author's note: the cover image for this story comes from the inimitable limey404, whose artistic ability deserves all due credit for decorating (and frankly, improving) my literary failure.

Dipper sneaked a glance back at his alarm clock and sighed upon seeing it was nearly one in the morning. Off to his left, Mabel was sleeping soundly – at least as far as he was aware. He was too absorbed in the latest product of the Sibling Brothers series to be sure. If she were snoring, it was too light to be heard over the steady rain that tapped on the roof above. The boy was adding his own instrument to that unrelenting symphony as he clicked at his pen; at his sister's request, he'd stopped thinking out loud, but the pen was a habit he was simply unwilling to part with. Just as he reached page two hundred and forty, a strange sound from her side of the room caught his attention. He peered through the inky darkness at first, unwilling to point his reading light that way for fear of blinding Mabel by accident. Silence reigned; after waiting a few seconds more, he issued a shrug and went back to reading.

"Dipper?"

His reaction to her voice was to abruptly drop his pen, although he did manage not to unleash a squeak of terror at being surprised. Clearing his throat, he turned the light so he could see her. "Did I wake you?"

Her face was oddly contemplative, certainly not a look he was used to her having. "No, I just had a thought and now I can't get back to sleep."

"Oh. You wanna talk it out?" he offered, taking up his pen.

She nodded curtly, blanket tugged up around her nose. "If you wouldn't mind."

"Of course not." Like a ninja, he drew a bookmark from under the sheet and stuck it in the open book. His light went dark, and after he put the whole thing aside, he laid down and assumed the usual Pines-twins-having-a-bedtime-conference position: hands clasped on his chest and staring at the ceiling. As his eyes adjusted to the pall, he glanced over and saw that Mabel had taken up the very same pose. "What's bothering you?"

She took a dramatically loud breath before speaking. "When do you think we'll get our fifth fingers and toes?"

He blinked at the question. The topic was in that category of background noise that everyone noticed but was never really bothered by, akin to the weather or the seasons. "I'm not sure. It usually happens not long after puberty."

Mabel shifted on her bed, accidentally nudging Waddles in the side. The oink of protest made Dipper snicker. "Sorry, guy." She got settled again and went back to addressing the topic. "Wendy doesn't have hers, and she's almost sixteen."

"Well, puberty ends at different ages for different people. Sometimes it can be as late as seventeen." He was thinking now, and that meant his pen-pressing thumb was hard at work.

His answer was not satisfying enough to prevent an annoyed grunt. "But why aren't we just born with them instead of having to make one later? Isn't that kinda dumb?"

Dipper smiled at her logic, which he quietly agreed with. He took a minute to frame as much of his explanation into Mabel-sized words as he could. "Humans have a weird form of latent, self-correcting genetic oligodactyly. It's nothing to worry about."

"We have a what of whatcha what whats?" Mabel blurted out, eyes bulging. "Bro bro, please use words that don't give me a migraine in the membrane."

Exactly the reply he expected, and yet he couldn't help but laugh again. "Sorry. What I mean is, virtually all of us have a condition where we're missing toes or fingers, but that fixes itself as we get older."

She nodded to herself, finally able to process his statement. "Ohhhhhhh. Wait, though. If we all end up with five fingers, why doesn't everybody end up with five toes? Grunkle Stan has as many as we do!"

He allowed his eyes to close as he listened to the rain. "It's different for everyone. Besides, even if you get a fifth toe, it's a useless pinkie one. We can move around totally fine without it, so it's not even a thing."

"Okay, I'm cool with that. I'm not cool with the fingers, though." Mabel let out a frustrated noise, then a subsequent one that seemed to Dipper to be rather anxious. "I'm just worried."

"Why?" he asked, tilting his head to look over.

"Is it...is it gonna hurt?" Even through the darkness, the nervousness in her glittering eyes was plainly apparent.

Dipper smiled one more time, although this was a grin of slightly amused empathy. "Nah. You know that weird space Wendy has by her ring fingers? We'll get one too, then it'll pop out there." She squeaked at his usage of the word 'pop'. "No no, it won't explode out of your hand like a horror movie or anything."

"Dang it, Dipper!" she growled, hurling her pillow at him. "You are not helping me with my finger worries!" They both laughed this time.

He tossed her pillow back and went about getting comfortable. "What I meant is, we're carrying the vestigial digit-"

She pounded her mattress to interject. "Easier words, dang it!"

He smirked to himself. "Sorry. We have the finger in our hands, but it won't get pushed out until later. It only hurts if there's a problem with the finger itself."

"Hrm. I guess that makes me feel better."

He nodded at her tone. The pregnant pause that chased her words lead him to believe the conversation was over, so he reached for his book. However, a bout of curiosity struck him. "Didn't you learn about this from that horrible book Stan made you – I mean me – I mean...you know what I mean – read?"

"No," she whined, hiding her eyes as if to stop the words from pushing up into her mind's sight. "That was just full of icky sweaty ew oh my goodness no no no no whhhhhyyyyyyyy stuff."

"Huh. I guess that's bad enough. I hope he doesn't make you read it again." Her pillow flew at him a second time. "Hey! I was being sympathetic!" He threw it back and pretended to be grumpy. "I try to help you calm down and you keep assaulting me? Thanks, Mabel."

"Aw, I just playin' with ya, Dippingsauce." Another pause followed this exchange. He took up the book and went back to reading, although through sheer force of will he stayed his pen clicking hand. Five minutes trundled past; by now he assumed she was sleeping again.

"Hey, Dipper?"

He looked over again, but the reading light left him unable to see for a few seconds. "What's up?"

"What are you gonna do when you get your finger?"

He let the book fall into his lap and rubbed at his chin. "Huh. I'm not sure. I could use the extra grip to try and open pickle jars, finally." He made a face at her peals of laughter. "Oh, shut up. Pickle jars are an evil invention meant to keep the people down."

Mabel was still giggling at him. "Sorry, bro. I have a better chance of bench pressing the Mystery Cart than you do of opening a pickle jar." This time, it was his pillow that covered the distance between their beds. "Ow! You jerky dumbface!"

"You really need to work on your insults," he snickered, snatching the pillow out of the air as she fired it back.

Her laughter grew so loud she had to cover her mouth with a hand. "I know it, man, I know it. Maybe Pacifica can give me lessons or something."

They shared another laugh before he went back to reading and she tried to re-fluff her battered pillow. He didn't get three more pages finished before looking back in her direction. "What'll you do with yours, Mabel?"

His eyes adjusted to the dark just in time to see a truly massive smile conquer her face. "That's easy, bro. I'm gonna shoot someone an official bird."