Look but don't touch? The very notion seems outlandish in the increasingly interactive world of contemporary art.
But that's the rule that has been imposed in Tate Modern's Turbine Hall.
The public was initially encouraged to stomp around to its hearts' content on Ai Weiwei's 100 million tiny porcelain "sunflower seeds". But the Tate gallery, alarmed by the potential hazards of the "dust" being thrown up by the public's feet, has imposed the no-contact restriction. Visitors will now have to admire the sea of seeds from a walkway above.
The Chinese artist's work is said to be a commentary on how individualism is crushed in his mother country. Though the handmade seeds look identical, no two are actually the same.
So we have a choice about how to interpret the Tate's move. Health and safety gone mad? Or an indirect warning to Beijing to stop walking all over the Chinese people? Let's be generous and agree on the latter.