GIVE someone who is sick a sugar pill that you have told him is a powerful drug, and it will often make him feel better. Even if you tell him what it really is, he may still feel better. The placebo effect, as this phenomenon is known—from the Latin for “I shall please”—is one of the strangest things in medical science. It is a boon to doctors and a bane of those running clinical trials, who must take account of it in their designs. But how it works is obscure. Read the rest at The Economist.