Eyrbyggja Saga - The Seal of Frodis-water
The house at Frodis-water is haunted by a group of undead fishermen and their leader, Thorir Wooden-leg. The hauntings escalate until a seal's head begins to emerge from the floorboards. Despite the inhabitants' attempts to smash it back down, the seal keeps rising until a young man uses a sledgehammer to drive it back, temporarily ending the phenomenon.