Makes you think....
1. I have known a pair of identical three-year-old twin boys. One had begun to stammer (stutter). After a few weeks, his twin began to stammer, too. But the first twin forbade it, saying, "No, you can't do it! Only I do it!" And his brother stopped immediately.
I do not know whether the second twin was simply copying his brother or whether his stammer was more genetically determined, but I think this case supports the idea that there can be an element of volition, at least in the early days.
2. A gentleman telephoned me because he wanted to know why he and his sister both liked to stutter (in spite of wishing to be rid of the problem too!) "Why do we enjoy doing it?" he asked.
I think this results from the compulsive element in stammering or stuttering. It is even possible that the build up and eventual release of a stammer could have an addictive aspect in some people.