"What's a twin?"

"A twin is a brother or sister that grew in the womb with you. Sometimes they look the same."

"What's grew in the womb? And I think we're defining 'brother' differently."

"The part of  (usually) a lady where babies grow. Don't you know anything?"

"She appeared fully formed three months ago, Veles, she kinda doesn't."

"I know plenty!" she says, and valiantly doesn't stomp her foot. "And I'd know more if you just told me stuff!"

"Put it this way. Kids usually start out... smaller."

"Thank you. And how's that work?"

"...You ever notice some kids are smaller than you? Or bigger?"

"...Yeah, come to think of it. They also all look different in lots of ways."

"You ever wondered what boy and girls were... for?"

"Those are really weird differences to have. But most of the variations don't seem to serve a purpose?"

"You know what an egg is? Ever seen like, a deer with a smaller deer?"

"Uh. I don't know eggs, but there's smaller of some animals, yeah."

"So, when the gods aren't just making them with Dice, most creatures propagate by this thing called mating. Basically, a boy animal mates with a girl animal, and then a really tiny version of that animal grows inside the girl until it's ready to come out. All the human boys and girls you'd know though will be too small for that for at least a few more years."

"...That is a really weird system. Why would you design a system like that?!"

"We didn't design it!"

"And our parents seem to like it."

"It's weird. I'd make a better one if I was doing a system."

"Well, long story short, boys and girls start looking way different after about year four, if they woke up on the bigger side."

"So kids are like little deer? What do really big kids look like, then?" It's a weird thought.

Veles picks up a handful of earth, and blows it into the air.

Which resolves into the image of a radiant, benign looking woman, young but motherly, with hair like the sun. 

"That's a grown up goddess," Veles explains.

"Why's she all stretchy? And lumpy!"