((Backdated to sometime during the holidays. I'd have put this up sooner except, well, I've been busy.))
Given how well it had worked
last year, Amaranth decided that spreading holiday saliva was a tradition that should continue for as long as possible.
Thus it was that, with the assistance of house elves, she made sure mistletoe was hanging above every frequently (and not so frequently) used door in the school. The mistletoe would be charmed to remain levitated over the school for a few days, which was certainly long enough, in Amaranth's view, for gratuitous snogging to commence.
Satisfied with her work, the nymph bounced gaily down the halls, eager to assist anyone should they find themselves in need of a makeout partner.