We can actually deduce here that the two interesting or unexpected details from Mann's description of pre-Columbian Native America is:
Charles Mann is actually known to be a science writer and a journalist who is known to have written "In 1491: New Revelations of the Americas Before Columbus". In the book, Mann actually shared previous reports from historians on the same issue but he further made new revelations and discoveries which were made available with the use of technology.
Mann actually took time to interview experts in the field and also traveled to significant places by himself in order to get adequate information.
Thus, we see here the interesting things Mann described in his book.
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