Chiquito only sees Olivier four times a year, but when he does, it's a very tactile meeting. He hugs Olivier. He grooms Olivier's hair. He sniffs his fingers after touching Olivier's chest, where spider monkeys have a scent gland. He licks the sweat on Oliver's forehead.
At four years of age, Chiquito is too strong and potentially dangerous to interact with Olivier without chain link between them. And were he so inclined, he could do serious damage through the chain link - but the only time he exhibits frustration (by showing his teeth) is when he has to let go.