In a hot car last summer queuing for an overdue ferry, a friend suggested a technique for such longueurs: start a chuckle chain. Wind down the windows, look meaningfully at one another and simulate laughter. "Heh!" ... "heh heh!" ... "Heh heh heh heh heh!" Once the whole car is rocking, the drivers of the vehicle in front will start to giggle; ditto the ones behind. Peering quizzically about to see what's so funny, tickled all the same, a line of five or six carloads can be animated in this way, without any having the faintest idea why.

I'd guess the French choreographer Maguy Marin knows this trick, because in the work she brought to Dance Umbrella she goes one further and extends the rhythm of laughter to the whole body. What begins as a single joke whispered by one dancer to another develops into tittery little steps, shoulder-shaking convulsions and then great head-flinging leaps, as one by one additional dancers are drawn to the source of mirth like streams to a river. After a few minutes the entire stage, and parts of the Queen Elizabeth Hall audience, are rippling with helpless good humour. It's actually a little unsettling, because these infectious emotions are hard to account for. And for the next 90, rather more sober, minutes, Marin's accomplished dance-theatre company conspicuously fails to shed any further light on them.

Maguy Marin belongs to that post-modern European school of dance theatre which has grown up in the shadow of Bejart and Bausch, and which too often falls prey to the belief that absurdity has meaning in itself. This show, for instance, was named Waterzooi after a Belgian stew - a gesture that is meaningless to the point of idiocy. Vignettes using dialogue, dance, and Denis Mariotte's charming nursery music are punctuated by a lecture from a woman behind a microphone, based on philosophical texts by Descartes, listing various emotions, their characteristics and effects.

"Anger" - or could it have been "Unease"? (we had to guess) is depicted by three men sitting at music stands tootling a canon on toy instruments. A dispute breaks out over the correct reading of a phrase, and after a long and heated argument in French over the musical distinction between a "croche" and a "triolet" (would the audience have submitted to this so willingly if they'd understood the paltry dialogue?), the arrhythmic player lands one of his fellow musicians a slap. The rest of the company appear and a full-scale epidemic of face- slapping follows. So much for "anger" - or "unease".

Another lengthy dialogue in French occurs between a barefoot girl in jeans and a woman in heels and a fur stole, hinging on the notion that the rich woman pays lip-service to the poor, but by a slick play of words is able to avoid recognising her culpability. This level of philosophical debate might have stood Marin well enough in her bac exam, but it doesn't cut much ice on an international theatre stage.

Marin's ideas improve when restricted to movement alone. There's an intriguing love duet in which the woman knots and unknots herself in ever more sinister ways around the man's upright body, as if terrified of touching the ground. And a full-company number in which groups walk in stooped, diagonal rows like factory workers in a Lowry street scene, wheezing on mouth-organs an eerie, drawn-out chord sequence which serves to emphasise their weariness, their little lives and even littler deaths. But over-repetition destroys the cleverest ideas. Marin has ignored one crucial emotion, and that's the spectator's ennui.

Wilful obscurity and head-banging repetition characterised the other Dance Umbrella offering last week, causing some members of the audience to stage their own mini-dramas in making for the exit. They should have stayed. Dutch company Raz's De Reis 2 (don't ask) tackles colonial attitudes in Africa, using just four performers, a large square of coir matting and 200 tins of sardines.

Choreographer Hans Tuerlings homes in on the complex mix of guilt and pathos in the white man's relations with black and vice versa. Thus his black man is a skinny white in a grass skirt, white socks and black lace- ups. Half tribal, half apeing his employers, his movements are a pathetic mishmash of simpering western classical, vapid disco dancing and ethnic thump. It's almost too painful to watch. The colonials - two men and a woman - are elegant, bored, sardonic. Dressed in sharp Yamamoto jackets, they lounge and sashay, toying aimlessly with the "black" man in a cruel parody of friendship. The show is hard on the eyes (lit by tropical white light) and even harder on the ears (one drummed rhythm repeated five million times). But you're left with a clearer vision of the murky and entrenched nature of racial unease.