The gelada has two threat displays: it raises its eyebrows to display the pink skin underneath, and it pulls its lip over its face to turn itself into a terrifying long-toothed demon.
Yeah, I’d lead with the lip thing, mate.
Geladas are very odd monkeys. Close relatives of baboons, they live only in Ethiopian mountains, they’re covered in shaggy yellow hair, and they’re the only monkey that primarily eats grass. They are like a cross between a cow, Animal from the Muppets, and your nightmares.
Actually, on a more contemplative note, this raises an interesting question: are non-human animals freaked out by faces without eyes? If this pinking-out-the-eyeballs thing is an effective threat display, maybe so!