"And you're both certain that no one ever sets foot in here?" Hermione firmly asked as she intensely and silently observed the concoction being stirred in a simmering cauldron with a silver spoon borrowed - more likely stolen - from the Hogwarts kitchen by Fred. "Not too much sulfur extract, George."
"Gotcha," replied George. He corked the glass vial and placed it back into his satchel.
"Believe us, Granger, anyone who's been at Hogwarts for at least two years wouldn't give a second's thought to setting foot in this particular lavatory," Fred confidently said, "and we have Moaning Myrtle to thank for that!"
"The sobbing wraith over there in that cubicle, I presume?" Hermione rhetorically responded as her gaze drifted to the weeping stall that contained the bespectacled ghost.
"Yes, Myrtle's just the sobbing wraith of Hogwarts!" she wailed. "Dead, dead, dead is all she is! Pay no heed to the fact that she's still human!"
Hermione rolled her eyes.
The three Slytherins were in the unutilized girls' lavatory on the second floor of the school; it served as a makeshift manufactory for the twins' prank paraphernalia. On their way to the lavatory, the twins told Hermione that, while they unctuously considered themselves clever, they felt that having a bright third party greatly familiar with the properties of many ingredients chaperoning the production of their items would be convinient.
The Ravenclaws would never think of "wasting their intellect on such childish things as the production of joke novelties"; the Hufflepuffs were horrible at keeping secrets, and the brothers would swim through raw sewage before they asked a favor of anyone from Gryffindor.
"That and we made a miscalculation in the measurement of a particular ingredient that resulted in pink bubbles spouting from our ears for two weeks straight, last year," George had revealed before they arrived.
"Dare I ask how these ingredients ended up in the possession of you both?" she had suspiciously questioned. But when mischief gambolled about in their eyes, Hermione sharply said, "Nevermind! The less I know, the better."
A little over an hour later the trio would sit upon the cold floor in the lavatory, working in tense silence; though students rarely set foot in Moaning Myrtle's lavatory, there was always the slim chance that a curious sound would summon an unbidden student or staff member - worst case of all, Filch and Mrs. Norris. Thus, they kept their ears open.
Hermione watched Fred raise the spoon from the cauldron, attached to it a stretching, taffy-like pink substance. "Ah, it's cooling just as you said it would, Granger! We could kiss you!"
"Do you want your lips hexed from your faces?" she jeered. "You both may want to consider finding a test subject for these...what do you call them again?"
There was a note of great pride in their voices when they simultaneously answered "Puking Pastilles!"
"Yes, yes. As I said, a test subject would be helpful in recording how fast the vomiting starts and how long it lasts, if you want to possibly moderate the ingredients to prolong the lifespan of the effect."
The boys nodded. "Since the ingredients combined make up both the product and its antidote, it would indeed be good to see how long it would take to neutralize itself. Question is: where are we going to find a willing guinea pig?" pondered Fred.
The boys looked at Hermione, who stood up defiantly. "Not even maybe; I said I would help with your novelties, but not as a test subject."
George groaned. "The teachers will question us if we start puking endlessly day and night. So who?"
Suddenly, her first night in Slytherin flitted into her mind's focus, followed by a particular Slytherin's still-vivid raving: "A MUDBLOOD! WE HAVE A MUDBLOOD IN SLYTHERIN!"
She experienced no rage at the recollection, and even sneered at the opportunity presented before herself.
"I nominate," she spoke, her voice fiendish, "Draco Malfoy."
Save Moaning Myrtle, all occupants of the lavatory sneered wickedly.