15. As well as food, wine features very heavily throughout the Seder. At one point, we dip our fingers into our cups and spill drops of wine on the table. How many times do we do this, and what does it represent?
From Quiz Symbols and the Seder
Answer:
13 times for the 10 plagues, and the 3 acronyms with their initial letters
The ten plagues that G-d inflicted upon the Egyptians were: water turning into blood, frogs, lice, flies, a disease which afflicted livestock, boils, burning hail, locusts, darkness, and killing of the first born (both children and animals). Before the arrival of the tenth plague, G-d told Moses to tell the Israelites to make a mark above their doors with lamb's blood, so that G-d would know to spare them.
The drops of wine also represent the blood spilled when the Egyptian army drowned in the Red Sea while chasing after the Israelites. By diminishing the amount of wine in our cups, we are also diminishing our celebration, as the Egyptians were G-d's creatures too.