You know Kari Byron and Tory Belleci from their work on the groundbreaking series “Mythbusters.”  They are now featured in a new Travel Channel show “Thrill Factor,” which explores the science behind thrill rides as they visit amusement parks across the country.  We had a fun chat about fear, monkey brains, screaming and how many times in a row one has to ride a roller coaster when shooting a TV series.