The one thing you mustn't expect from the London International Mime Festival is common-or-garden mime. What you can expect to encounter is the power of suggestion in every form: the aliveness of puppets, the mobility of masks and the sheer amazingness of the human body.

But I'm still puzzling over what we were expected to find worth watching in this year's contribution from Belgium's Compagnie Mossoux Bonte. Last festival the group produced a series of blackly comic sketches involving a solo performer with a spooky tendency to sprout prosthetic heads. Virtuosic, provoking, the show opened up all kinds of philosophical trapdoors: what the new "theatre of images" does best.

In the company's latest production, The Last Hallucinations of Lucas Cranach, the audience finds itself confined for an hour to looking at one room of an art gallery - the sort that's kept in darkness for fear of fading ancient pictures. "Watch this space", it says. But watching paint dry would have been a welcome distraction.

On the Purcell Room stage is a black wall, inset with alcoves framing live mock-ups of portraits by one Lucas Cranach the Elder (1472-1553). Cleverly reproduced and lit, Cranach's glowing paintings beam out the standard 16th-century virtues of purity and propriety. I'm not familiar with the chap in a Flemish hat pictured eyeballing a fish, but in my art- historical ignorance I accept its veracity. The other subjects are less ambiguous: a lady in a red gown reading a book, another in a fetching Bo-Peep straw hat. Respectable? Moral? Pah! say Mossoux Bonte, determined to find the cracks in the paint that will show medieval life to be venal, violent and vile.

We look. The portraits look back. Then, after some sinister, buzzy organ music, they start to do things. It's hard to say quite what. Quivering, fidgeting and simpering, tiny movements that might be accidental if they weren't the sole focus of attention. After a very long time, as if sensing our exasperation, the woman with the book snaps it shut. The man starts to nuzzle the fish. Bo Peep has climbed into another girl's picture-frame and they are snickering together. Lady in red now rips off her clothes and holds a dagger at her own throat. Go on, do it! you urge. Just please make something happen!

It doesn't. We cut to a familiar tableau of Adam and Eve (not a stitch on, but we are spared their blushes for their heads are out of the frame). Eve, struggling with the world's first case of delirium tremens, tries to palm off the apple with a shaky dilatoriness that should have roused instant suspicion in her mate. The show ends as the entire set of portraits step out from their frames and approach the audience with a rather futile air of menace. If the sins of the flesh were as unappetising as this, I'm not surprised old Lucas Cranach stayed on the side of the angels.

It was some relief to turn, at the ICA the following day, to the exquisite decorum of Stephen Mottram's Animata. Here the prosceni- um is tiny - just two feet by three - and the players finely crafted anatomy mannequins, operated by strings or clockwork; yet with such miniature means Mottram transmits some very big ideas based on Richard Dawkins's book, The Selfish Gene.

Mottram's biology lesson takes the form of a series of glimpses into a merciless world where society exists only to promote natural selection. His tiny critters are preyed on, "harvested" by a superior species for the precious seed found within their bodies. The survivors, over time, adopt increasingly complex disguises to avoid capture - a brilliantly coloured coxcomb, an amphibian's shell, extravagant extra joints to their limbs.

It's hard to know precisely why we can be so affected by marionettes, but even this dispassionate parable pricks ducts you didn't know you had. The puppeteer's physical presence on stage (tree-trunk legs and feet, sometimes a helping hand - unwittingly, of course, he's God) touchingly conveys his own affection for his tiny charges. They are indeed very beautiful in their intricacy. When the predator (a larger, goat-faced thing) snatches up an automaton to put in his sack, the poppet struggles so convincingly that - ridiculously, for a moment - you are outraged by this casual cruelty. And all the while Glyn Perrin's appealing electro-acoustic score is setting out the drama's global and timeless span - eternity, no less. The secrets of DNA explained in 55 minutes: you'd scarcely think it possible.

London Int'l Mime Festival continues to 26 Jan. Information: 0171 637 5661.