Any doubt concerning afflictions [of tzaraas] at the outset is tahor as long as it has not been confirmed to be tamei. Once it has been confirmed to be tamei, a doubt [is ruled to be] tamei.  A zav is checked in seven ways as long as he has not been confirmed to [be tamei] from zivah —- concerning food, drink, carrying a load, jumping, illness, sight, and thought. Once he has been confirmed [to be tamei from] zivah, we do not examine him —- his mishap, or doubts because of his seminal discharge are tamei, since the matter is indicated.  [If] someone struck his fellow and they assessed that he would die, but [his condition] improved from what it had been. After that, it worsened and he died —- [the attacker] is liable. R’ Nehemiah says: He is exempt, for the matter is indicated.