Scientists have created the first molecule that can move in a straight line by itself on a flat surface by mimicking how a person walks. The molecule—9,10-dithioanthracene, or DTA—is made of a coal-tar derivative linked to a pair of sulfurous organic compounds. When heated, the linked compounds moved in alternation so only one was lifted from a copper surface at a time. The planted “foot” kept the molecule from stumbling or veering off course, even when pushed or pulled with a fine probe.