Hair

Dis spent her girlhood fascinated with her brother's hair.  Her own took after her mother's; Father, tousling their blonde heads, laughed and called them the truest gold in Erebor.  Thorin, on the other hand, came crossly into the world with a thatch of jet black curls that made his lumpy infant self look like the monkey a merchant from Dol Amroth had brought their grandfather.  

Dis found him almost mesmerisingly ugly, and, even as newborn hideousness grew into chubby childhood, she decided he made a far better playmate than any doll.  Dwarves breed more prolifically than elves, but that doesn't take much, and rank always comes with distance, so Dis often had been lonely, and found in this strange little creature that squawked and grumbled delightedly when she dressed him up and inexpertly dressed up his hair - first by sticking in it baubles and bits of jewelry, and then, as it lengthened, braiding in little lengths of silver chain, often distracting herself halfway through by comparing its curlier texture and shining darkness to her own blonde waves - a great satisfaction.

Years passed and he grew into a fine child, quieter than most (this worried their parents a little) but as inquisitive and bull-headed as one could wish for.  To Dis's delighted amusement, the sturdy little boy shadowed her not only in her escapes and explorations, thus getting doubly under the adults' feet, but also, when someone managed to rope her into them, to classes.  

He'd lurk under her desk and she'd pretend to take notes while secretly teaching herself Rohirric knotwork via his unruly black mop, until, at last, some strange twist of his little-boy brain made him wonder what would happen if he bit her engineering tutor's bum.  Dis had never guessed the extent of the old woman's obscene vocabulary, far less heard even a quarter of the words she used.

That would have been all right, but that Thorin, the little parrot, peered inquisitively up at the tutor - who stared at him in towering indignation over her immense bosom - and repeated, all cheerful innocence, the choicest of those terms.  She dragged both of them (Dis found this immensely unfair) before Thrain, by the ear.  Thorin got smacked soundly on the bum as a lesson in empathy, but Dis got forbidden his company for a whole fortnight, as punishment not only for skiving off classes, but for being sneaky about it and giving her brother a bad example.

It was a few weeks thereafter that Dis quite accidentally swapped out her favourite toy for a little brother.  Grandfather had been treating with a goblin king - goblins, like dwarves, make no distinction in rank between genders - who wore woven into her wiry grey hair a truly extraordinary hat composed, so far as Dis could tell, of a nest of live buzzards.  King Zhikar's mountain boasted a great fissure from peak to upper caverns, which Erebor lacked, with the tragic consequence that Dis's closest approximation of the majestic carrion-birds was a flappingly indignant rooster.

This time, nobody had to drag the king's grandson before the throne.  He galloped right into the Great Hall in a cacophony of bellowing, shrieking and crowing, trailed closely by feathers and distantly by Dis.  She got hided this time, and Thorin didn't let her touch his hair for thirty years.