The Mishna on today’s daf contrasts between two methods of ritual slaughter of birds – sheḥita (ordinary ritual slaughter) and melika (pinching – slaughter performed as part of the Temple service). According to the Mishna if sheḥita was performed by cutting the back of the neck, it is invalid, while if melika was performed in that manner, it is valid; on the other hand if melika was performed by cutting the front of the neck, it is invalid, while if sheḥita was performed in that manner, it is valid.
Sacrifices brought from fowl are not formally zevaḥim, a category limited to animals that are slaughtered in an ordinary fashion. Birds are prepared for sacrifice by means of melika, where the kohen pierces the neck of the bird with his fingernail (see Vayikra 1:14-17 and 5:8-10). The Gemara in Massekhet Zevaḥim (daf 64b) describes melika as one of the most difficult of the services in the Temple, and explains what was involved.
Rav is quoted by Rav Zutra bar Toviyya as teaching that the kohen would hold the wings with two fingers and the legs with two fingers stretching out the bird’s neck, and the bird would be killed by means of the kohen‘s thumbnail. According to the baraita, the bird’s body was held in such a way that it was outside the hand of the kohen, and – while holding the wings with two fingers and the legs with two fingers – the kohen would kill the bird with his thumbnail.
According to Rav Ovadya mi-Bartenura , as well as the Rambam, the kohen would hold the bird in his left hand according to one of the two opinions, and would perform melika with the thumb of his right hand. This parallels cases of slaughter in the Temple, where both hands are used. The Shita Mekubbetzet quotes Tosafot as suggesting that the entire melika service was done with the right hand (as depicted in the above illustrations). According to this approach we can easily understand why this service is considered to be the most difficult one, since the bird had to be held and killed with a single hand.