Katrina Brooks has felt overwhelmed lately. She runs a small business in Austin, Black Pearl Books, and late in the spring, she started to receive so many orders that she wondered if they might be fake. The numbers were massive, six or seven orders a minute. At one point, she asked her husband if he thought an automated bot could be artificially inflating their sales. It wasn't. Support for the Black Lives Matter movement had surged. A pandemic-frozen world erupted in outrage over the deaths of George Floyd, Breonna Taylor, Ahmaud Arbery, Mike Ramos and more — Black Americans killed at the hands of white police officers or vigilantes...