MSG stands for monosodium glutamate. It is a natural, but nonessential amino acid. It is used by food manufacturers as a flavor enhancer, and by itself has the taste of “umami”—the fifth taste sensation we mentioned in “Macroscopic Properties: The World We See.” There have been countless studies on its safety to eat, and the data overwhelmingly supports MSG as being safe to consume even in absurdly large quantities. But don’t try to disprove those studies—everything in moderation—your mother was right about that.