Torah Temimah cites Toras Kohanim (Sifra, Vayikra Dibbura DeChovah, Section 9).
Sefaria — Toras Kohanim (Sifra, Vayikra Dibbura DeChovah, Section 9)
“And he shall not sever” — therefore, if he did fully sever (completely separate the head from the body), the offering is invalid.
Miyut from the negative command “lo yavdil” — complete severance of the head is disqualifying.
In melikah of the bird-chatas the head must remain attached. If the kohen fully severs the head from the body, the offering is invalid. The Torah’s explicit “and he shall not sever” is not merely descriptive; it sets the boundary of a valid service.