Bridget Riley

Ever stood in front of a Bridget Riley op-art painting? I went to an exhibition of her stuff at the Serpentine Gallery in Hyde Park once. The paintings are huge, they take up an entire wall. Stand in front of them and stare for too long and suddenly everything goes all wibbly - all you can see is black and white lines and they shimmer and start to move of their own accord. Her paintings are quite literally staggering - it's hard to stay upright while looking at them.