The blond Slytherin was surprised when Emma went and sat down on the chair. She wasn't putting up a fight! Feeling more confident about her ploy, she cast a charm that made the ropes tie themselves around the other girl's body, from shoulders to her legs. Putting the blindfold on over Emma's eyes, she made sure it was completely covering before moving to stand behind the chair.
"We just have to get through this," she whispered to the brunette.
With a flick of her wand, she weaved an illusion. This time of Mrs. Norris the cast scrambling out from the interior of a student's desk and padding her way towards them. As the cat moved closer, it shifted into the form of a spindly, severe looking old woman with high cheekbones and grey hair tied up in a bun.
"An apt sentiment, Miss Greengrass," the illusion spoke in a piercing German accent. "Vor vee next hour, you vill both belong to me," she informed them with haughty cruelty. "Now Miss Greengrass, lay on your stomach across Miss Rosier's lap and raise your skirt."
Astoria began to stammer a question, earning herself a sharp retort from the fake teacher. Doing as the illusion had instructed, she cast another charm to tighten the blindfold flat against Emma's face, so there could be no peeking. Yet another spell launched Emma's wand from hiding to sail across the room, hitting the wall and clattering to the floor. Once she was laying across Emma's lap, she lifted her skirt, sliding forward so her ass was further up in the air as if she had been pushed forward.
"Oof!" she exclaimed softly for added effect. "Now Miss Rosier...I vill vr-ee a hand and vet you begin to punish Miss Greengrass vith ten spanks. You may begin veen your hand is vr-ee. Proceed slowly," the illusion spoke in slow, measured tones as Astoria used magic to unwrap Emma enough that one arm was free.