This term refers to two very ancient divination arts. There’s even a verse in the Bible that mentions gastromancy.
One of these two methods is used to look into the future and is related to the behavior of water. It is also known as lecanomancy.
Numerous candles were lighted and placed behind glasses of water. The seer would then call a young pregnant woman or a child and ask a series of questions.
The woman or child would answer accordingly with what
they thought they could see inside the glasses. They were
looking at images formed by the refraction of the candlelight.
Other ways of practicing lecanomancy were by interpreting the shape of a flame when a lit candle was placed inside a round crystal container filled with water; also the sound of rocks or shards thrown into water containers was interpreted.
Lecanomancy in its three forms is therefore one of the two forms of gastromancy. There is, however, one very peculiar method that was based in divination by use of a person giving voice to spirits. Puppets are as old as the first civilizations and they were thought to have divination ability. Ancient Greece was one of the first civilizations to have puppets. Eurycles of Athens became very famous for his ventriloquism or gastromancy, as this kind of divination art required that the practitioner was a ventriloquist. Candles were lit and placed around one of the water containers. Then the spirit was summoned and the water was made to unsettle and splash by moving the containers. The spirit usually did not take long to answer in a deep and cavernous voice coming from the stomach of the sorcerer or seer who was conducting the divination. His or her lips would not move. Only the voice was evident.
These sorcerers and practitioners believed that the summoned spirit answered questions from his eternal dwelling.
As another example in ancient Egypt, where gastromancy was also practiced, it was believed that spirits lived underground. The sorcerer was believed to pick them from under the ground and into his or her body, and expel them through his or her mouth at the moment of telling the answers in a loud voice.