Knife in the Clear Water

In the far mountains of Ningxia province, the old Ma Zishan and his son start mourning his wife. Loved by everyone in the village and the family, the son wants to sacrifice their only bull for her 40 days disappearance ceremony. Zishan isn’t against it, but his sorrow and his love for the old animal make him wonder. Even his prayers and the Imam don’t seem to erase his doubts. Until one morning the old bull stops eating and drinking. Has he seen the knife in the clear water?