Here Thoth is placing an Ankh at the mouth. The Ankh is the symbol of eternal life. The gods are often seen holding an ankh to someone's lips this is considered to be an offering of "The Breath of Life". The breath you will need in the afterlife.
Thoth
Other Names: Tehuty, Djehuty
Patron of: knowledge, secrets, writing, and scribes
Appearance: A man with the head of an ibis holding a scribe's palette and stylus. He was also shown as a full ibis, or sometimes as baboon.
Description: Thoth is an unusual god. Though some stories place him as a son of Ra, others say that Thoth created himself through the power of language. He is the creator of magic, the inventor of writing, teacher of man, the messenger of the gods (and thus identified by the Greeks with Hermes) and the divine record-keeper and mediator.
Thoth's role as mediator is well-documented. It is he who questions the souls of the dead about their deeds in life before their heart is weighed against the feather of Maat. He was even sent by Ra to speak with Tefnut and ask her to return when she abdicated her position and went to Nubia. He is also the great counselor and the other gods frequently went to him for advice.
Thoth is considered a lunar deity and is often depicted wearing the lunar crescent on his head. There is a story told of how Thoth won a portion of Khonsu's light, and this may be the reason. As a lunar deity his totem animal is the baboon, a nocturnal animal that goes to sleep only after greeting the new day.