Salt water - reminds them of the tears they cried in Egypt. Haroset - nut, apple, cinnamon, wine mixture which has the appearance of straw in remembrance of the mortar used to build the Treasure Cities for Pharaoh. It is symbolic of the hope of freedom that enabled their ancestors to withstand the bitterness of slavery. Matzah - the unleavened bread that reminds them of the haste with which they left Egypt. After the drinking of wine and washing of the hands the greens are dipped into the salt water and eaten.
Half remains on the plate, half is hidden for the dessert.
This is to keep the interest of the children. Children are to find it and keep it till the end of the meal when the leader redeems it in exchange for the promise of gifts. Throughout the service many things are incorporated to keep the interest of the children. The most important thing is the telling of the story of the Exodus to the children. The telling of the story of the Exodus includes everyone's favorite part - the 4 questions, asked by the youngest child present.