The ceremony of the opening of the mouth

This ceremony was performed after the funeral cortège (see lower register) had reached its destination. Its purpose was to return to the deceased the use of his organs in the Afterlife. He had to be able to feed himself, recite magical spells, give commands and see. 

In the case of statues of gods it was generally performed in the House of Gold, i.e. the atelier of the sculptor and goldsmith. The eyes and mouth were 'cut' open with a stp (setep) adze, thus enabling the god to see, speak and eat, and at the same time enabling all the other senses as well. The psS-kf (pesesh-kaf) was possibly used to cut the statue's umbilical cord symbolically, the last act of giving birth. In the Pyramid Texts it is used to prepare the mouth:

"O King, I fasten for you your jaws which were divided - psS-kf."

Faulkner: Utterance 37/30a:

Upuaut was the god of Lykopolis and had the form of a jackal. As a martial Opener of the Path his attributes were a mace and a bow. He was Leader of the Gods and his standard was first in royal processions. He preceded even Osiris and two of his standards were carried at the head of the funeral cortèges. Placed in the grave he guarded the deceased.

O King, I open your mouth for you with the adze of Upuaut… Horus has split open the King's mouth, using that with which he split open his father's mouth, using that with which he split open Osiris' mouth, with the iron which issued forth from Seth, with the adze of iron which split open the mouths of the gods.

A model of a calfs leg is instrumental as well, though its purpose is unclear. The ceremony is very ancient, dating to the Old Kingdom, though details are known only since the New Kingdom.
An important part of the ceremony were the offerings which the deceased would need in his afterlife. Loaves of bread, cakes, beer, fruit and vegetables, oil, fowl and meat carried in them a life force which could be extracted. 

The mummy was also annointed. Seven different kinds of oil were used for this purpose, setji heb, hekenu, seftji, nekhnem, twat, hatet ash, hatet tjehenu. The sem-priest offered the vessel and the kher-heb spoke the words:

"Osiris Unas, I have filled thine eye for thee with metchet oil."
"Osiris Unas, there hath been presented unto thee that which hath been pressed out from thy face."
"Osiris Unas, the Eye of Horus hath been presented unto thee, and [Set] hath been made weak in respect of thee thereby."
"Osiris Unas, the Eye of Horus hath been presented unto thee, that it may unite itself unto thee."
"Osiris Unas, the Eye of Horus hath been presented unto thee, that the gods may be brought unto thee thereby."
"O ye Oils, O ye Oils, which are on the forehead of Horus [place ye yourselves on the forehead of the Osiris Unas, make ye him to smell sweet in possessing you], make ye him to become a khu (i.e., Spirit) through possessing you, make ye him to have his sekhem (i.e., Vital Power) in his body, make ye him to have openings before his eyes, and let all the khu (i.e., Spirits) see him, and let them all hear his name. Behold, Osiris Unas, the Eye of Horus hath been brought unto thee, for it hath been seized that it may be before thee."

The Papyrus of Unas

E.A. Wallis Budge The Liturgy of Funerary Offerings, pp 88ff