Disappearances!
It wasn't exactly a normal morning at Hogwarts School of Witchcraft and Wizardry. It was Valentine's Day, and that meant deliveries. Also couples acting like couples, even at breakfast, not to mention the occasional couple who had got into a fight at the dance the night before and were now spending breakfast sulking and sneaking glances at their former boyfriend or girlfriend to make sure they were noticing exactly how much they weren't paying attention. And then there were those people who hated Valentine's Day studiously ignoring anything that looked in the least bit Valentiney.
So it wasn't exactly a normal morning, but it was a pretty typical morning. That changed at precisely 8:21am, in the middle of breakfast. Suddenly, with no fanfare at all, a large fraction of the students in the school disappeared.
In the normal world, those professors who were at breakfast started bustling around, talking to each other in low voices and trying to maintain order amongst the shocked students, eventually sending some of their own to track down students in other parts of the castle and delegating prefects to do what they could with keeping order in their houses.