This happened in Vinland Saga episode 19. After a duel between Thorfinn and Thorkell, Canute came and made some contract with Thorkell to join his side. Thorkell agreed with that, and out of nowhere, Askeladd laughs. What's the reason for Ashlad laugh at that time because there was nothing funny at that scene?
You could watch the episode on Youtube at 06:35