Describe symbolism in The Demon-Haunted World by Carl Sagan

Sagan does not use symbolism in the book. He does, however, note that there are faith healers, who decided on their career direction after witnessing the power of the human mind to believe in the face of the unbelievable. These healers recognize the strength of suggestion, which is symbolized by the placebo, or sham treatment that seems to bring relief as the sufferer believes it will work