1. One is required to eat Matzah Shemurah for the Mitzvah of Matzah.
2. An item of clothing containing any amount of Sha'atnez may not be sold to a Nochri.
3. Based on this law (#2), Rava issued a ruling about a boatload of wheat that had sunk.
4. There is a dispute in the Mishnah about putting flour into mustard or Charoses.
5. Rav Kahana explains that the dispute in the Mishnah (#4) refers only to mustard.
A BIT MORE
1. Accordingly, one may not use Matzah baked by Nochrim for the Mitzvah of Matzah, even if he is sure that it did not become Chametz during the baking process (and it is Kosher).
2. Even though a Nochri is not commanded to observe the laws of Sha'atnez, he might sell the garment to a Jew who will not be aware that it is Sha'atnez.
3. Rava ruled that one may sell only a small amount of wheat to each Jewish customer, so that he definitely will use it all before Pesach (since the wheat is Chametz).
4. Tana Kama: One should not place flour into mustard or Charoses, and if he did he must eat it right away. Rebbi Meir: The mixture is forbidden.
5. Rav Kahana says that everyone agrees that if flour is placed into Charoses, it should be burned immediately. A Beraisa that supports Rav Kahana's explanation.