Some thinkers require a minimum of three parts in a body, appealing to the three dimensions: length, breadth and depth. On this view, two parts do not yet establish the entire dimensional character of body.
Length: extension in one direction.
Breadth: extension in a second direction.
Depth: extension in a third direction.
The argument needs examination: can merely counting three parts establish three dimensions, or does their arrangement matter? Number of constituents and geometric extension are not the same question.