* Happiness: Smiling, relaxed lips, and open eyes.
* Fear: Wide eyes, open mouth, and sometimes a furrowed brow.
* Anger: Lip retraction, teeth bared, and sometimes a furrowed brow.
* Sadness: Depressed facial muscles, downturned lips, and closed eyes.
* Surprise: Wide eyes, open mouth, and raised eyebrows.
Additionally, they use facial expressions for:
* Social communication: To signal dominance, submission, or interest in mating.
* Threat displays: To warn other monkeys of potential danger.
* Grooming: To show affection and build social bonds.
* Food solicitation: To communicate their desire for food.
While the exact meaning of some expressions may vary across monkey species, facial communication is an important part of their social lives. They use a complex combination of facial expressions, vocalizations, and body language to communicate effectively.