translation.en: But the third challenge we have -- and probably even bigger one, the biggest challenge -- is that, in contrast to smallpox where you could always see your enemy -- every single person almost who was infected with smallpox had this telltale rash.
translation.zh: 我们当时面临的第三个挑战 很可能是最大的一个挑战 与天花作战时，我们总能看清敌人 几乎每个感染天花的人 都会长出明显的疹子