Hello Knockturn, I want to remind everyone that casting rictusempra in the Great Hall / Entrance Hall is NOT allowed. I've seen many people do this before. When they cast on someone, they give me the excuse saying "I had his/her permission"
We don't care if you had their permission to cast on them, what happens if you miss and cast on someone else? Points would be taken is what happens. It just seems easier to not cast that spell at all in the Great Hall. In fact, it was said that no spells should be casted in the Great Hall. But this topic is just focusing on the fact of Rictusempra in the Great Hall.
To sum it up: DO NOT CAST RICUTSEMPRA IN THE GREAT HALL