A spider monkey is chained up below a hotel terrace, kept as entertainment for guests. The speaker watches him swing for hours, mechanical and tireless, "as if driven by hidden gears & springs." Then the speaker sits down nearby, and the animal changes: he stops, climbs up, and holds out a hand for food or trinkets. The speaker feels a mix of pity and goodwill, guessing that anything might relieve a life of boredom, and starts digging through pockets.
The mood turns on the word "until." What looked friendly becomes alarming once the monkey wraps himself around the speaker's leg and won't let go. It takes half the staff to pull him off. The final image, a bite that "still stings" days later, leaves a lingering discomfort. The poem suggests that captivity warps the creature, and that the speaker's casual sympathy is tangled up with the same amusement that keeps him chained.