A bracket-style competition by public vote to choose the Smithsonian Institution’s “most iconic” object has led to a barrage of competitive tweeting and Photoshopping, as a Pullman train car races against the original “Star-Spangled Banner” flag, and a Tyrannosaurus rex skeleton battles the National Zoo’s young panda (“Bao Bao may be small, but at least she’s not extinct.”) and the space shuttle Discovery (“What is black and white AND has been to space? Not Bao Bao.”).