A dragon is a Mythical Animal. Many dragons were bat-winged dinosaurs. that breathed fire. Europeans saw dragons as dangerous, frightening monsters but Chinese mythology sees dragons as powerful protectors.
Believing in dragons is about as sensible or as silly as believing in Crocoducks (although dragons make SLIGHTLY more sense). The film "Dragons: A Fantasy Made Real" gives us a scientific hypotesis on dragons. It tells us that dragons could fly and breathe fire through the use of hydrogen, methane, and platinum.