If a firstborn fell into a pit, R’ Yehudah says: An expert may go down and look [at the blemish]. If [the expert finds that] it has a blemish, he may bring it up and slaughter [it]. But if not, he may not slaughter [it]. R’ Shimon says: In any case where the blemish was not detected before Yom Tov, it is not considered to be prepared.