Something weird happened last week. It was something that millions of people who have faced years of painful prices at the gas pump never expected: The cost of a barrel of oil dropped into the negatives. Today, we explore why this happened, and what it reveals about the state of the economy. Guest: Clifford Krauss, an energy correspondent for The Times based in Houston. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: The bizarre dip in oil prices was based on a quirk in the way barrels are traded, one that appears only when the market is “undergoing extreme stress.”“I’m just living a nightmare,” one leader of a large petroleum association said. This is a look inside how the pandemic is decimating the oil industry.