Regarding the preparation of the bitter herb for eating, the Mishnah clearly states (Siman 576, sif 36): "And behold, in our countries the other species are not found, and therefore the bitter herb commonly eaten in our country is lettuce, which is the chazereit. And one must be careful not to eat it whole, as it is almost dangerous and not a mitzvah, for due to its bitterness it can cause great harm. Therefore, one must crush it with the yad, and present it in this manner, and then its bitterness dissipates. The GRA (Gaon Rabbi Eliyahu of Vilna) was accustomed not to crush it before bringing it from the synagogue, so that the taste does not dissipate, for then one does not fulfill the requirement with it, but rather should crush it after bringing it, cover it until the beginning of the Seder, and when Pesach falls on Shabbat, crush it in advance, place it in a vessel, cover it until the beginning of the Seder, and then scatter it on a plate. Through this, its bitterness dissipates, and then one should dip it, and estimate that it is the size of an olive, and one can eat it with relish."