What's killing all the people in this exclusive book trailer for Rick Yancey's The Fifth Wave?

Rick Yancey's The Fifth Wave is one of the summer's buzzed-about young-adult debut novels, and we're debuting an exclusive book trailer right here on io9. The "first wave" wiped out half a million people. And you can see here what the second wave does. What do you think the fifth wave is? »4/09/13 7:53pm4/09/13 7:53pm