Atlantic bluefin tuna has been so overfished that some sushi chefs are looking at unusual alternatives. We'll find out whether deer and horsemeat might turn up in sushi anytimes soon. Also: a look at how our borders and boundaries have shaped this country's sense of identity. Then we'll take a tour of some of the historic landmarks that are tucked away all over New York state, from Long Island to the Finger Lakes. And just in time for the Fourth of July: Please Explain is all about fireworks.