Ai Weiwei sunflower seeds.
For two and a half years, 1600 Chinese artisans took on the task of hand making one hundred million porcelain sunflower seeds. These seeds were for the artist Ai Weiwei and in October 2010, 150 tons of them were installed in the Turbine Hall at Tate Modern in London. The opening of the installation allowed visitors to interact with the seeds; they could walk on and amongst them.

This changed after 48 hours when dust from the ceramic seeds was deemed a health hazard and the piece was roped off.

These seeds were acquired from an anonymous source and are probably a little bit stolen.

Ai Weiwei predicted this would happen. Perhaps that's why he had so many made.