832. The Shankbone and the Egg; Leaning
118:5 After the destruction of the Temple, the Sages instituted that two types of food be on the table during the reading of the Haggadah, one as a reminder of the korban Pesach (the Passover sacrifice) and the other as a reminder of the korban chagigah (the Festival sacrifice), which are brought at a time when the Temple is standing. (We use both items even when yom tov falls on Shabbos, despite the fact that the korban chagigah was not brought on Shabbos - Mishnah Brurah 473:22.) It is customary that one of these items be meat from the shoulder, which serves as a reminder that we were redeemed by G-d "with an outstretched arm." (If one doesn't have this, he may use a different cut of meat - MB 473:27.) It should be roasted on coals as a reminder of how the korban Pesach was roasted over fire. The second item should be an egg because egg in Aramaic is "bei'ah," which is similar to the word meaning to ask, since we should ask G-d to redeem us. The egg can be roasted or cooked in water.
These two items must be prepared before yom tov. If one forgot to do it, or if the day before yom tov is Shabbos, then one may roast and cook them on yom tov night but he must then eat them on the first day of yom tov. Similarly, he may roast and cook again on the second night but he must eat them on the second day of yom tov. This is because we may not cook on one day of yom tov for the next, nor may we cook on yom tov for a weekday. Since we don't eat roasted meat on the two Seder nights, we must eat the shoulder during the day. Even though it was roasted before yom tov, we don't throw it away. Instead, on the second day of yom tov, we put it in the food we are cooking and eat it.
118:6 One should prepare his seat for the Seder during the day with the nicest cushions as his means allow. Things should be arranged so that he can lean and recline on his left. Even if one is left-handed, he leans to the left, not on his own weaker side. (After the fact, if a left-handed person leaned on his right, he has fulfilled his obligation - MB 472:11.) The Seder plate should also be arranged while it is still day so that when one comes home from shul, the Seder can start without delay.