A year before his death in 1996, the beloved American cosmologist and author Carl Sagan wrote The Fine Art of Baloney Detection—the best 20th-century essay on the subject of bullshit. “In the final tolling,” he wrote, “it often turns out that the facts are more comforting than the fantasy.”

Citing aspirin commercials, Whole Life Expos, the use of dousing rods to find mineral deposits and “psychic surgeons” to cure all manner of disease, Sagan addresses the “steady rainfall of deception” that moistens modern life. “These,” he writes, “are all cases of proved or presumptive baloney. A deception arises, sometimes innocently but collaboratively, sometimes with cynical premeditation. Usually the victim is caught up in a powerful emotion—wonder, fear, greed, grief. C...