Kommentar zu Zevachim 6:4

היה מולק את ראשה (pinch the bird’s neck with the finger nail) – he would hold its two wings with his two fingers the span from the little finger to the thumb of a spread hand and a fistful of the meal-offering in his left hand, and the bird on the side of his hand and the face of the bird to the side of the back of his hand, that the neck would be above, and he stretches/extends its neck of the throat on the width of his two fingers, the index finger and the arm and he pinches with his finger nail. And this is one of the hardest forms of Divine service that is in the Temple.

How was the hatat of a bird sacrificed?
He pinches off its head behind its neck, but he did not sever it.
And he would sprinkle its blood on the wall of the altar.
The residue of the blood was drained out on the base.
Only the blood belonged to the altar, while the rest of it belonged to the priests.
Our mishnah continues to provide instructions as to how the bird hatat was sacrificed.
Section one: Birds are not slaughtered to be sacrifices in the same way that birds are slaughtered to be eaten. To make a bird kosher, the shochet slices its neck, the same way that he does for an animal. But for sacrificing, the priest pinches off its head off with his thumbnail from the back of the bird’s neck. See Leviticus 5:8-9. He does not sever the head entirely from the body, just separates it by pinching it off.
Sections two-three: After pinching off its head, he sprinkles the blood out of the bird onto the wall of the altar. Note that its blood is not received in a ministering vessel. The residue of the blood is squeezed out of the bird onto the base of the altar.
Section four: The rest of the bird was eaten by priests only the blood was put on the altar.

ואינו מבדיל – [and he doesn’t separate] the head from the body, but rather severs the spinal column and the nape and most of its flesh is with it until he reaches the gullet or the windpipe and takes one organ alone and pinches the bird’s neck with his finger nail, as it is written (Leviticus 5:8) “[He shall bring them to the priest, who shall offer first the one for the purification offering, pinching its head at the nape] without severing it.” (see Talmud Zevakhim 65b)

ומזה מדמה – he holds the bird/fowl and sprinkles. For he does not sprinkle neither with a utensil or with a finger, but with the body of the bird/fowl.

היה מתמצה (drains/empties out) – that he offers up the place in the bird’s neck to the altar and presses it on the wall and the blood drains out and goes down to the base [of the altar]. For regarding the sin-offering of the fowl/bird, it is written (Leviticus 5:9): “He shall sprinkle some of the blood of the purification offering on the side of the altar and what remains of the blood shall be drained out at the base of the altar,” Which wall do the remnants belong to and he drains out the blood to the base of the altar? I would say that this is the lowest wall, that is from the red line and below, for if it was the upper wall, that is from the red line and above, sometimes it (i.e., the blood) would drain out to the surrounding ledge, for since he would make it above the surrounding ledge that the red line is below the surrounding ledge by a cubit.