James had arranged his classroom a little differently in order to perform the demonstration required for the lesson that day. The desks has been pushed to the side and cushions had been laid out on the floor in front of his desk with enough for one per student. As they began to enter the classroom in droves he turned his attention to them, "Come in, everyone take a seat we're mixing things up today," So far they had been reviewing old concepts in preparation for their exams but today they would be learning something new and that required a demonstration, something he hoped they would enjoy even if it wasn't the most practical of spells.
"Today we will be learning the Gemino curse," James said once he had closed the classroom door and leaned against his desk. "This curse is slightly different to what you've learned about so far as it does not directly cause harm to a person or an object, when the spell is cast on an object it will duplicate when touched, the copies of the item are however useless," He paused before continuing. "It might not seem that useful to you however it is often used as a security measure for high value items in Gringotts, items duplicating endlessly in a confined space will certainly have consequences for anyone foolish enough to attempt a break in. This spell should not be confused with Geminio which duplicates the targeted object as Geminio is not a curse, and it makes a double in appearance, and any magical effects it contains will not be duplicated. The doubling charm has the same name, yet, how to make it into a curse is a special case." James took out his wand and from his desk took a plate which held a single cookie on it. He cast the Gemino curse on it and touched it so it duplicated and passed the plate to the first student. "As you can see after casting the curse and touching the cookie it duplicated, I want you each to touch the cookie and watch as it duplicated and pass the plate on once you've seen it," James stood with his wand ready in case things got out of hand, but he had made sure the demonstration would be entirely safe. One by one new cookies emerged and by the time the plate made its way back to him it was full. He tapped his wand on the cookie to stop it duplicating and set the plate on his desk.
"I think that's enough for one day, I'll let you go and enjoy your free time before your next class, don't say I never give you anything, and speaking of, for homework please write an essay about the curse we covered today and why it's dangerous due next lesson, class dismissed,"
RP the lesson. Do the homework for extra credit. First poster feel free to have your character be the first person to be handed the plate.