Scenes from the confrontation late Friday, which also appeared in videos uploaded to social media, captured the attention of Venezuelans, many of whom blame the unpopular president for the country s food shortages.In one video, Mr. Maduro tries to calm the pot-bangers by walking among them, only to be surrounded as the furious crowd yells obscenities. What is this?  an astounded voice behind the camera asks in one of the video clips.Mr. Maduro had traveled from the capital, Caracas, to Margarita Island off Venezuela s northern coast to inaugurate a number of new public housing units and give a televised address.During the speech, he denounced his opponents  calls for his removal from office, calling them  vampires  and saying they were preparing for violence.Foro Penal, a Venezuelan human rights group, said 20 people had been arrested after the protest in the island town of Villa Rosa. Mr. Maduro s office made no statement about the episode.