Answer: Dirty socks
Billy told Sam that he smelled like dirty socks. When Sam demanded that Billy put an alert out for the virus because, according to Sam, the virus is coming to America, Billy said, 'What about Lassa in '89?', and Sam said, 'I was wrong'. Then Billy said, 'What about Hanta in '94?', and Sam said, 'I was wrong'. Then Billy said, 'But you're right about this?', and Sam said, 'No, I could be wrong'.