A kohen whose sister dies... Recognizing that kohanim don't become impure in mourning anyone other than the 7 relatives, but the sister seems to be an exception, that her status has impact on his becoming impure on her behalf. Why her status makes a difference is not clear. Also, the case of a convert before the age of 3 years and one day, who is considered fit to marry a kohen, whereas older converts are not. Which also raises a lot of questions. Plus, the example from the war in the Book of Numbers, and the special way they determined who was fit to join the Jewish people then.