A machloket between Abaye and Rava with regard to conspiring witnesses -- whether such a witness is disqualified from that moment onward, or also retroactively for any previous testimony. Note also that this is one of the rare (6) cases where the Halakhah follows Abaye instead of Rava. Also, the disqualifications based on close family relationships. Plus, another version of the list -- Rabbi Akiva's simpler list, which is not used as such. Plus, love and hate may disqualify, just on the strength of those emotions, it would seem. Until the Gemara posits that the Jewish people would not stoop to that kind of bias.