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מסכת חולין פרק א משנה ד
השוחט מן הצדדין One who slaughters from the sides [of the neck],
שחיטתו כשרה his slaughtering is valid;
המולק מן הצדדין one who performs melikah from the sides,
מליקתו פסולה his melikah is invalid;
השוחט מן הערף one who slaughters from the back of the neck,
שחיטתו פסולה his slaughtering is invalid;
המולק מן העורף one who performs melikah from the back of the neck,
מליקתו כשרה his melikah is valid;
השוחט מן הצואר one who slaughters from the throat,
שחיטתו כשרה his slaughtering is valid;
המולק מן הצואר one who performs melikah from the throat,
מליקתו פסולה his melikah is invald;
שכל הערף כשר למליקה because the entire back of the nקck is valid for melikah
 וכל הצואר כשר לשחיטה and the entire throat is valid for slaughtering.
נמצא  Thus,
כשר בשחיטה פסול במליקה what is valid for slaughtering is invalid for melikah
כשר במליקה פסול בשחיטה and what is valid for melikah is invalid for slaughtering.
 

משנה ה;

כשר בתורין

What is valid for turtledoves (i.e. the stage at which the bird becomes mature enough to use as a korban)

פסול בבני יונה is invalid for young pigeons (as at that stage this particular species is deemed too old to be used as a korban),
כשר בבני יונה what is valid for young pigeons (i.e. the stage of youth at which this species can be used as a korban)
פסול בתורין is invalid for turtledoves (for being too young);
תחילת הצהוב the beginning of the yellowing (of the neck of the bird, which is a sign of its undergoing a transition from youth to maturity)
בזה ובזה פסול by both [renders them] invalid.

 

Notes

המולק - This is a method by which a bird being sacrificed as a korban would be slaughtered.  When performing מליקה, a kohen would pierce the back of the bird's neck with his right thumbnail, severing its spinal cord and the majority of either the esophagus or trachea.