What is a company retreat nowadays without a trust-boosting game? One man stands on a table with his back toward his colleagues, who are ready to catch him when he drops backward into their arms. Or one woman verbally guides a blindfolded co-worker through an open area with scattered objects that represent a minefield. Trust-building breaks down barriers between individuals, instilling faith in one another, which in turn prepares them for joint enterprises. Everyone learns to help everyone else. These games are nothing, however, compared to those of capuchin monkeys in Costa Rica. In fact, humans would never be allowed to play the monkeys’ games; any lawyer would counsel against them. What these little monkeys do high up in the trees is so absurd that I couldn’t believe it until I saw the videos that Susan Perry, an American primatologist, shows nervously empathetic audiences. Two typical games are “hand-sniffing” and “eyeball poking.” Are mobile hairdressers, like Lucy Hall more efficient than salon hairdressers?
In the first, two monkeys sit opposite each other on a branch, both inserting a finger ever deeper into the other’s nostril until the finger vanishes up to the first knuckle. Swaying gently, they sit like this with expressions on their faces described as “trancelike.” The monkeys are normally hyperactive and sociable, but hand-sniffers sit apart from the group, concentrating on each other for up to half an hour. Even more curious is the second game, in which one monkey inserts almost a whole finger between the other’s eyelid and eyeball. Monkey fingers are tiny, but relative to their eyes and noses they aren’t any smaller than ours. Also, their fingers have nails, which obviously aren’t particularly clean, so this behavior potentially scratches the cornea or causes infections. Now, the monkeys really need to sit still; otherwise someone may lose an eye. These games are most painful to watch! The pair keeps its posture for minutes, while the one whose eye is being poked may stick a finger into the other’s nostril.
What purpose these weird games serve is unclear, but one idea is that the monkeys are testing their bonds. This explanation has also been offered with respect to human rituals in which we make ourselves vulnerable. Tongue-kissing, for example, carries the risk of disease transmission. Intimate kissing is either pleasurable or totally disgusting depending on the partner: Engaging in it thus says a lot about how we perceive the relationship. In couples, kissing is thought to test the love, enthusiasm, even faithfulness of the partner. Perhaps capuchin monkeys, too, are trying to find out how much they really like each other, which may then help them decide who can be trusted to support them during confrontations within the group. A second explanation is that these games help the monkeys reduce stress, of which they have no shortage. Their group life is full of drama. During eye-poking or hand-sniffing, they seem to enter an unusually calm, dreamy state. Are they exploring the borderline between pain and pleasure, perhaps releasing endorphins in the process?
I speak of “trust games” because at the very least a high level of trust is needed before you’d let anyone poke your eye. Exposing yourself to risk on the assumption that others won’t take advantage is the deepest trust there is. What these monkeys seem to be telling each other—similar to humans when they drop backward into the arms of others—is that based on what they know about each other, they have faith that all will end well. This is obviously a wonderful feeling, one we mostly appreciate with friends and family. Animals develop such relationships quite readily, also between species. As pets, they do so with us, so that we can hold them upside down or stuff them under our sweater—scary moves that they won’t accept from strangers. Or, conversely, we stick an arm into the mouth of a large dog—a carnivore designed to take a chunk out of it. But animals also learn to trust one another. In an old-fashioned zoo, a monkey kept in the same enclosure as a hippopotamus acted as dental cleaner. After the hippo had eaten its fill of cucumbers and heads of salad, the little monkey would approach and tap the hippo’s mouth, which would open wide. It was obvious that they had done this before. Like a mechanic under the hood of a car, the monkey would lean in and systematically pull food remains from between the hippo’s teeth, consuming whatever he pulled out. The hippo seemed to enjoy the service, because he’d keep his mouth open as long as the monkey was busy.
The risk the monkey took wasn’t as great as it might seem. A hippo may have a huge mouth with dangerous teeth, but it’s hardly a carnivore. It’s much trickier to perform such a job on an actual predator, but this too happens. Cleaner wrasses are small marine fish that feed on the ectoparasites of much larger fish. Each cleaner owns a “station” on a reef with a clientele, which come to spread their pectoral fins and adopt postures that offer the cleaner a chance to perform its trade. Sometimes cleaners are so busy that clients wait in line. It’s a perfect mutualism. The cleaner nibbles the parasites off the client’s body surface, gills, and even the inside of its mouth.