*First question: What causes stuttering?* Answer: [This](https://i.imgur.com/MAjzt1b.png) research could shed some light to the cause of stuttering. (Kenneth J. Logan-Fluency Disorders\_ Stuttering, Cluttering, and Related Fluency Problems; 2017, p. 205) *Second question: where does our brain fail to send the message, where is the problem happening exactly. What is the biological and psychological cause or disposition to stuttering?* You will find the answers to your other questions from page 46 onwards (in the book: Ehud Yairi\_ Carol H. Seery-Stuttering \_ foundations and clinical applications; 2023) See my PM.