Firstly, our Avestan mss do not represent the fragmentary remains of the huge canon of twenty-one
Nasks ("the Sasanian Avesta") described in the ninth-century Denkard, but rather they contain complete liturgical collections that were employed in ritual and in the training of priests.
Assuming, therefore, that the ritual may have been one similar to the sidos rituals, the mahr, i.e., Avestan text, recited at this ceremony may have been the Ustauuaiti Ga[theta]a, which is recited by the soul while still sitting near the place where the person died (Hadaxt
nask 2.2), and, specifically, its last had, the Kamnamez had, which is said in the S(t)udgar
nask in book nine of the Denkard to be "about the coming of the Bone-untier," i.e., when a person dies.