The review says that "most estimates of the frequency of human sacrifices in Tenochtitlan come from an unfounded assertion by the Franciscan friar Diego Valadés, who was born twenty-two years after the city fell. Valadés claimed that between 15,000 and 20,000 people were sacrificed in Tenochtitlan per year." Later, "Cortés’s confessor and the first formal historian of the Conquest of Mexico, raised the figure to 50,000."
"The number is remarkable for how preposterous it is: more than 137 sacrifices a day, five an hour, one every twelve minutes, twenty-four hours a day. Aztec sacrifice was a nonmechanized process that demanded extensive ritual preparation and an individually selected victim, and archaeologists have never found evidence to support the Spaniards’ figures. As [the book's author] points out, although human skulls have been retrieved from ritual burial grounds close to Tenochtitlan’s Templo Mayor (the city’s main temple), most of the sacrificial remains that have been found belong to animals—wolves mostly—and these remains don’t add up even to hundreds of victims, let alone thousands."
Also, regarding cannibalism, "owing to a [Spanish] royal law from 1503, an enemy fighter who practiced cannibalism could be enslaved for life, and shortly before Cortés left Cuba for Mexico a smallpox epidemic caused a drastic reduction in native manual labor in the Caribbean. The later narratives that were so insistent on the subject of cannibalism are always, in [the author's] view, related to the conquistador generation’s claim to cost-free indigenous servitude. This argument became especially important after the Crown abolished native slavery and gave indigenous subjects rights identical to those of Spaniards in the New Laws of 1542."