There is nothing like opening of the mouth.
The 'wp r' opening of the mouth ceremony (or ritual) was an Ancient Egyptian ritual described in funerary texts such as the Pyramid Texts.
Egyptologists misinterpret the above hieroglyphs as 'opening of the mouth'. The correct word of Sanskrit is Shri-nga J`Uxk means 'horn' and next glyph is for 'r'. Thus the complete conjunctive word is Shri-nga + r J`Uxkj meaning 'A fragrant for dress or body, to make up, adornment of body. This refinement was ritual. The word 'Shri-nga-r' is to make up a live or dead person.
Guessing to see the open horns means 'opening of the mouth ceremony' is wild.