The iconic gathering of the secret society. The ritual's music is disturbing, as is the very mysterious nature of the event.
During the opening ritual of the gathering, a masked couple on the balcony stare down at Bill suspiciously. Done in POV, it arguably gives the illusion that they're staring right at the viewer.
The tense scene at the end of the gathering when Bill is outed as an uninvited guest, with all of the masks suddenly turning inquisitorially at him (with the angles and red-ish lighting making them look even more ominous/demonic). And the ominous Ligeti music playing over the scene really doesn't help.
