Scientists Henri B. Kagan and Kenso Soai have won the Nobel Prize in chemistry for untangling mysterious mirror images in molecules, a discovery that has been used to develop countless drugs and transformed modern medicine. Many molecules come in versions that look alike but are not exactly identical, like right and left hands. When designing drugs to treat diseases, scientists want to be choosy about which mirror image they get. Kagan, who is from France, and Soai, from Japan, found ways to make chemistry pick a side, designing and describing reactions to produce the desired mirror image.