This week's Please Explain is about the largest mammals on earth: whales. Joining us are: Dr. John J. Flynn, the Frick Curator of Fossil Mammals at the American Museum of Natural History and the Dean of the Museum's Richard Gilder Graduate School. He's also the curator of the exhibition "Whales: Giants of the Deep," on view at the museum through January 5. And Dr. Mark Baumgartner, Marine Biologist and Associate Scientist at the Woods Hole Oceanographic Institution in Massachusetts.