The Allies dropped over 5 million bombs on Nazi Germany. One out of every ten didn't explode. The men of bomb disposal teams in Germany risk their lives every day to eliminate these dangerous remnants of war. 5,000 undetonated ordnances are found per year and tens of thousands of people are evacuated. In Germany, bomb disposal services clear an average of 100 World War II bombs per week.

Leading scientists and researchers weigh in on the scenarios that might unfold if aliens find us and decide to visit Earth. Should we even be searching for extraterrestrial life? What are the risks of reaching out, and what are the risks if the Earth is "found" by aliens?.