This week "Sunday Morning," with host Jane Pauley, features Susan Spencer's cover story on the benefits of afternoon naps. (Watch out for the boss!) Plus: Tracy Smith sits down with the Dixie Chicks; Luke Burbank interviews teen pop singer-turned-actress Mandy Moore, star of "This Is Us"; Martha Teichner looks back at the 1918 flu pandemic; Mark Phillips meets the dancers of "Riverdance," which is marking its 25th anniversary with a new production coming to New York's Radio City Music Hall; and Tony Dokoupil talks with photographers from the Louisville Courier-Journal, whose archive of pictures detailing the public and private moments of the city's most famous son are now collected in a book, "Picture: Muhammad Ali."