To create the effect of "teary eyes" when Ragnar is crying on the beach, Vaseline was smeared on the lens around Travis Fimmel which made everything around him appear blurry.
The chant heard on the score during the battle is lifted from a Norse poem known as Darraðarljóð, the song of darts. The poem is a gruesome description how Valkyries, lesser corpse goddesses in the service of Odin, weave the fate of a battle.
The filming location of Kattegat is north shore of Lough Tay in County Wicklow. It has green woodlands to the east and a scree slope to the west. The rapidly changing background often feels like a filming error when it isn't and is the same throughout all seasons. In this episode for example, the law-giver's rock is located at the base of the scree slope.