Remembering the bitterness of the story, we eat bitter herbs:

בָּרוּךְ אַתָּה יי אֱלֹהֵינוּ מֶלֶךְ הָעוֹלָם, אֲשֶׁר קִדְּשָנוּ בְּמִצְוֹתָיו וְצִוָּנוּ עַל אֲכִילַת מָרוֹר

Blessed are you, God, who makes us holy with your good rules, including the eating of bitter herbs.

haggadah Section: Maror
Source: The Minimalist Haggadah by Jon Kessler