Famously itinerant, and disdaining the whole notion of studio-based practice, Gabriel Orozco has always performed a high-wire act. And in the first room of his current show at the Serpentine Gallery, we find ourselves colliding with five bizarre clusters dangling on thin wires from the ceiling.
They are called Mixiotes, a term referring to a traditional Mexican recipe for cooking rabbit meat wrapped in leaves. No attempt has been made to guard their manifest frailty with a protective barrier. We are free to walk among them, puzzling over their unpredictable blend of cactus leaves, rubber balls and plastic bags. Gently revolving in the summer light, they look pale and crumpled. But after a while, Orozco's heretical combination of organic and artificial materials starts to acquire its own peculiar fascination.
Each of the balls - just the right size for kids to play with - adds a different colour. And because the clusters hang at different heights, they appear to be dancing up and down in space. They generate a feeling of childlike delight, until you realise with a start that the balls could easily be seen as heads. Once you read them this way, the clusters bear an uncanny resemblance to falling, inverted figures - eerily reminiscent of the despairing people who tumbled through the Manhattan air after the twin towers were set ablaze.
Orozco thrives on ambiguity. Sometimes he points to irreconcilable meanings in the title of a work: one seemingly lyrical and seductive sculpture, evoking the pleasures of the seashore, is called Floating Sinking Shell. As soon as we notice this contradictory name, the whole work takes on a more unsteady significance.
However, this remains far less haunting than the human skull covered in graphite markings. The careful task of drawing this grid of neat black forms all over the cranium took him six months to complete. On one level, the outcome seems harsh and relentless, encouraging us to explore every fissure and making us wonder at the depth of the empty eye cavities. The skull appears surprisingly small and even more frail than we might expect. Although plenty of real teeth still jut out defiantly from the mouth, they clearly belonged to an elderly person. It is a memento mori of the most disconcerting kind. Just as we recoil, another interpretation suggests itself. Orozco calls the work Black Kites, and the graphite forms ranged over its surface do also have a transcendent quality. They could be suspended just above the cranium, and hint at the notion of a soul escaping from the body after death.
Ever open to fresh possibilities, Orozco sets no arbitrary limits on what can be used in art. At one point in the show, we discover him venting an obsession with circular forms on collaged airline tickets. The tickets encourage us to see the painted orbs as images of Planet Earth. And when we come across a series of small works on graph paper called First Was the Spitting, Orozco makes us conscious of his own dried saliva. His toothpaste spit is scattered across each sheet in pale brown orbs. Only after a while do we appreciate how cunningly they are accompanied by tiny droplets of dark ink, building into clusters that look like grand architectural ensembles viewed from above. Or planets orbiting in the cosmos.
Unlike so many artists, smugly serving up the same formulaic concoction time and again, Orozco refuses to repeat himself. We can never guess what is coming next.
Suddenly, he confronts the viewer with an installation called Lintels, where ragged pieces of fuzzy grey material dangle from horizontal wires slung across the gallery. They reminded me of washing lines, and it turns out that the grey fragments are lint culled mainly from the artist's own laundry. Because they are all dry, the dishevelled pieces look abandoned - as though someone had simply forgotten to take them off the lines. The lint is so sensitive that it rippled excitedly when I breathed on it. Nothing could be more vulnerable than these desperately thin stretches of material, so exposed that they threaten to disintegrate and blow away.
Even at his most energetic and inventive, Orozco cannot prevent himself conveying profound misgivings about contemporary life. Towards the end of the show, there are two soccer balls placed on a white plinth. Orozco has incised them with interpenetrating circles, blithely expressive of his most cosmic fantasies. But the act of cutting into the balls has, inevitably, made them sag and crumple. Inviting us to dream about planets spinning in the solar system, they are nevertheless brought to the very edge of collapse.
"Gabriel Orozco" is at the Serpentine Gallery, London W2 (020 7402 6075) until 30 August
Richard Cork's earlier writings on Orozco are included in his four paperbacks on modern art, recently published by Yale University Press