The Greengrass sisters get their revenge

        Carving runes into acorns took a little longer than expected, since Oleandra decided to add the Fehu rune once they were halfway through, so by the time Oleandra and Daphne had arrived at the forbidden corridor, Harry, Hermione and Ron had already passed the first gauntlet by putting Fluffy to sleep with a flute.

Oleandra would never have imagined that the dog's weakness was music, just as its ancestor Cerberus had once been put to sleep by Orpheus's magical music. She might have known about this, had she continued on to muggle secondary education, but it was just not meant to be.

The sisters were fairly sure that the giant dog, like many fantastic beasts of its size, must possess considerable magical defences, otherwise Hagrid might as well have chosen his dog Fang as the first guardian. To fight against the dog, they had to use physical means, just as Weasley had crushed the troll's skull with its own club.

"Here's the plan," whispered Oleandra to her sister as they stood before the door that led to Fluffy. "I will attract the dog's attention, while you use the Levitation Charm to make the mutt swallow an acorn. Once you get one in, I'll activate it, then while it's incapacitated, you fly two more into its other mouths. Got it?"

Daphne nodded, and they split the acorns between the both of them. Oleandra took a deep breath, then opened the door, which strangely enough wasn't locked.

"HEY! YOU BIG MANGY MUTT. REMEMBER ME?" Oleandra screamed at the dog at the top of her lungs, while Daphne sneaked to the side.

Fluffy let out a load roar with all three of its mouths, sending spittle flying. Oleandra discreetly let a few acorns fall from her hand in front of her. She suddenly felt a lot less courageous, and a lot queasier. That dog had a very bad case of halitosis, one of its many weapons, it seemed.

Oleandra sent red sparks flying into its eyes. This was in no way a damaging spell, she only wanted to get it to charge. Fluffy was enraged. No one had ever treated it so rudely before. It shrank back, then pounced on her with all the grace of a rubbish lorry.

Oleandra was ready for this, her hands moving rapidly with the ease that can only come from hours of practice, as her fingers formed the letters B and F, the hand signs for the Berkana and Fehu runes! Berkana was also the rune of trees, and Fehu represented abundance and growth!

"Berkana, let my seeds beget a world of trees! Fehu, let the sturdy oak grow healthy and strong!"

Tall oak trees burst out from the acorns on the ground, taking root in the stone floor and piercing the ceiling. The giant dog crashed into the solid tree trunks, which held firm!

As the dog lay stunned from its head first crash into the trees, a voice was heard from a corner of the room.

"Wingardium Leviosa!" cried Daphne.

She outdid herself, as three different acorns flew into each of the dog's mouths and down its throats.

Oleandra repeated her hand seals, while chanting.

"Berkana, let the new grow from the old! Fehu, let the hardy oak grow unyielding roots!"

The gigantic three-headed dogs paused in its tracks, its angry growling turning into high-pitched yowls as it rolled around in pain.

The oaks' root system was penetrating the dog's tissues, drinking its blood, absorbing its strength. Then, Fluffy's fur seemed to bubble and stretch in some parts, as if something pointy was trying to escape from its body. When its skin could take no more, trees emerged from its head, throat and stomach, piercing through its dense hide, sending a spray of blood flying through the air.

The gigantic three-headed (or was it tree-headed, now?) dog lay dead, a canopy of blood-red leaves hanging ominously over its body.

Victory! The Greengrass sisters had finally achieved their vengeance over the nasty creature that had terrified them at the beginning of the year!

After a quick high-five, the sisters searched around the room, eventually finding a trap door where the dog had originally been lying down. Oleandra peered down through the hole. There was no ladder to climb down, only darkness. Who knew how deep this went?

After a moment of thought, she fetched a piece of bark and inscribed Kenaz, the torch rune on it. Then, she let it fall through the hole, letting it illuminate the way down.

"Look!" cried Daphne. "Down there!"

A squirming mass of vines shrank away from the shining piece of wood, letting it fall further down. The light soon disappeared.

"The Devil's Snare!" the twins said together.

"The dog must have been the gamekeeper's guardian, so this one must be Professor Sprout's!" said Oleandra.

They both jumped down the trap door, landing into the Devil's Snare safety net. This plant hated heat and light, so with a double "Lumos!" it had soon let go of the pair, letting them fall further down.

"There's a passage over there," observed Daphne. "It looks like we're going even deeper."

Oleandra frowned. How were they going to get back after this? She hoped there was a way out at the end.

After a short walk, they emerged in a room full of flying, winged keys. At the opposite side of the room, an open door, with a key still in the lock. Three broomsticks had been abandoned in a pile near the exit. At least they would be able to fly back out through the trapdoor, Oleandra noted with relief.

"I daresay we aren't the first ones here," remarked Daphne.

Oleandra's heart sank.

"It must be those three," she said through gritted teeth. "At this rate, they'll beat us to the stone!"

"Let's take the brooms," suggested Daphne. "We'll go faster riding those."

The twins grabbed a broom each and flew through the open door, trying to catch up to the Gryffindor trio.

As they approached the end of the corridor, they knew they had caught up, since they heard a voice:

"That's chess!" snapped Ron. "You've got to make some sacrifices! I make my move and she'll take me — that leaves you free to checkmate the king, Harry!"