The outbreak of bird flu currently tearing through the nation’s poultry is the worst in U.S. history. Scientists say it is now spreading beyond farms into places and species it has never been before.Emily Anthes, a science reporter for The Times, explains.Guest: Emily Anthes, a science reporter for The New York Times.Background reading: Scientists have faulted the federal response to bird flu outbreaks on dairy farms.Here’s what to know about the outbreak.For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.