Bava Batra 66 - A Mortar that was Carved then Attached to the Ground
One who sells a house has sold the mortar - if that mortar was carved in a stone that formed part of the house's wall. However, if the mortar was made from an unattached piece of wood or stone and then attached to the ground, such mortar is not included in the sale.
Rabbi Eliezer says, "Anything attached to the ground is considered as the ground. Therefore, he has sold the mortar."
What would the Sages say in regard to food placed on this mortar if the mortar is ritually impure? Is it part of the house and thus part of the ground for ritual laws, even if not for commerce, and then the food is pure, or is the mortar not part of the ground for both selling and ritual, and the food is impure? - This remains unresolved.