This is a time-lapse video of a crystal growing on a water droplet, as imaged using a confocal microscope. The crystal is composed of colloidal particles 1 micrometer in diameter (about 1/100 the width of a human hair, and 10,000 times larger than an atom). On a flat surface, the small growing crystallites could merge together to form a large domain, but on the curved surface of the droplet, the pieces cannot fit together -- just as strips cut from a sheet of paper cannot perfectly cover a ball. As a result, the crystal forms ribbon-like domains that branch from one another. The effects of curvature on growth may be relevant to understanding the self-assembly of curved nanoscale objects, such as viruses. This video relates to a paper that appeared in the Feb. 7, 2014, issue of Science, published by AAAS. The paper, by Guangnan Meng at Harvard University in Cambridge, MA, and colleagues was titled, "Elastic Instability of a Crystal Growing on a Curved Surface."