The source is an excerpt from the book "Underestimated" by J.B. Handley and Jamison Handley, which documents the Handley family's journey to help their son Jamison, who is nonverbal and autistic, learn to communicate using a letterboard. The book shares the family's experiences with various interventions, including FMT (fecal microbial transplants), and highlights their encounter with Elizabeth Vosseller, a therapist who developed a method called Spelling to Communicate (S2C). The authors also discuss the controversy surrounding S2C and its efficacy, challenging the assumptions and practices of the medical and educational communities when it comes to supporting nonverbal autistic individuals. The book concludes with a hopeful message that promotes understanding and acceptance of nonverbal autism and its potential for communication and growth.