Bishop Heahmund suddenly seems to speak the viking language, but in episode 10 he couldn't. He could only speak in his tongue with Ivar.
When Rollo arrives from Normandy, his ships are rowed into Kattegat. However, unlike viking ships, Norman ships could not be rowed. They could only be maneuvered with their sails.
Bishop Heahmund repeatedly says, his faith forbids him to marry. Celibacy was not introduced for the clergy until the 12th century.