Different parts of the body have religious symbolism. For example, the human foot, because it touches the dust of the earth, is used to symbolize humility and willing servitude. The heart is considered to be the source of understanding, love, courage, devotion, sorrow, and joy. The skull symbolizes the transience of life and the contemplation of death. It is the symbol of Hermits and Penitents, such as St. Mary Magdalene, St. Paul, St. Jerome, and St. Francis of Assisi. Hermits are usually shown with a skull to suggest their contemplation of death. When a cross is represented with the skull, it suggests their meditation upon eternal life after death. For more examples, you can find a "SYMBOLISM" attribute in most charm listings.