It was believed that when a person died, the soul had to pass through a dangerous underworld known as Duat where it faced all sorts of dangers like monsters and lakes of fire. The final and ultimate test for the spirit's voyage through Duat was "The Weighing of the Heart" which is illustrated below. The ba of the dead person is watching the test, hoping to pass. Anubis stands under a scale and verifies that it's working correctly as the ibis-headed scribe god Thoth waits to record the results. The heart of the dead person is weighed against "the feather of truth," a symbol of Ma'at (the goddess of truth, justice, and order). If the heart weighs less, the spirit is free to go on to meet Osiris in the afterlife. But if the heart is heavy with sin, it is thrown to Ammut, "the devourer of the dead," who gobbles it up, denying the spirit an afterlife and causing it to cease to exist!