After stemming historic protests across Cuba by shutting down digital communications this week, the island’s beleaguered Communist government is now beefing up a more traditional way of stifling opposition — citizen spies. The rapid-response brigades, which are made up of civilian snitches — neighbors, co-workers and plainclothes cops loyal to the regime — are out in force after protesters demanding food, medicine and freedom took to the streets beginning July 11, according to dissident bloggers on the island. Cuban journalist Yoani Sanchez reported an increase in the activity of the brigades, and “a heavy police presence” on the streets of...