One who plows a grave thereby creates a beis hapras. How far does [his plowing] make [a beis hapras]? A furrow’s length, which is one hundred cubits, an area of four se’ah. R’ Yose says: An area of five [se’ah]. [This applies] to a downward slope, but on an upward slope [the following procedure determines the size of a beis hapras]: A quarter [kav] of vetch seeds are placed on the knee-shaped part of the plow. Up to the place where three vetches will sprout alongside one another is deemed a beis hapras. R’ Yose says: [The law of beis hapras applies only] to a downward slope, not to an upward slope.