This is the statute of the Torah that the Lord has commanded, saying: Speak to the children of Yisrael, and they shall take to you a red heifer, perfect, in which there is no blemish, and upon which a yoke has not been laid.
Torah Temimah: Sotah 46a — A blemish disqualifies it [the para], but a blemish does not disqualify the eglah arufah.
English: In it a blemish disqualifies, but a blemish does not disqualify the eglah arufah.
Contrast between the two red-animal rites derived from the explicit “ein bah mum.”
The para aduma is invalidated by any blemish, whereas the eglah arufah (decapitated calf) is not subject to the same blemish disqualification.