Tosefta Sukkah 3:2 lists “18 days and one night” when we recite the series of Psalms known as Hallel. The one night, namely the first night of Pesach (and second, in the diaspora) jumps out as the occasion that is different from all other days when Hallel is recited. The Mishna in Pesachim chapter 10 describes the placement of this anamolous Hallel during the course of the Seder, and highlights other details of its recitation that differ from the typical recitation of Hallel, and Tosfot Sukkah 38a offer one more. Why is this Hallel different from all other Hallels?
We will find clues in several places, including Pesachim 117a, Arachin 10a-b, and more.
And we will be one step closer to raising our cups in song as we experience the Exodus anew at our seder tables.