(Bamidbar 19:16) "or the bone of a man": This refers to a limb (cut off) from a living person. — But perhaps it refers to a bone the size of a barley-corn? "and upon him who touched a bone" already speaks of a bone the size of a barley-corn. How, then, are we to understand "or the bone of a man"? As referring to a limb (cut off) from a living person. And two "bones" are being spoken of, viz.: "or the bone of a man" — a limb (cut off) from a living person "and upon him who touched a bone" — a bone the size of a barley-corn.
What Bone of a Man Makes You Ritually Impure
Sifrei Bamidbar 127:2