From the time my twin sons learned to talk until their first years in grade school, they struggled with a couple of different speech difficulties. When they were in first grade, the school did an assessment and recommended speech therapy for them. They both had the sibilant S lisp, and in addition, L-Y replacement. (Yes, not only do they look alike, but they talked alike too.)
My brother had the same issue, and my sons’ speech therapist told me that specific kinds of speech disorders are actually hereditary, so the predisposition was present in their genes, poor guys.
This resulted in some very interesting conversations when the boys were four or five, such as when DS B told someone to “Get a yife.” Or when, in an argument with someone (about the availability of cake, as I recall), he stomped his foot and barked, “Read my yips!”
They managed to surmount the L-Y hurdle (as did my brother), but they weren’t particularly compliant with their speech homework, so they’ve both still got residual S sibilance. Both them have first names that end with S (although DS B has adopted a nickname that ends with K instead). Poor DS A has both a first and middle name ending in S—obvious poor planning on our part as parents.
Because of my experience with my sons, I gave Riley Morrel, my folklorist hero in Stumptown Spirits, mild rhotacism—the inability or difficulty in pronouncing the R sound. People familiar with Bugs Bunny cartoons sometimes refer to this as the “Elmer Fudd” syndrome, since that character had a similar speech disorder. Most of the time, Riley consciously tries to avoid words containing the letter R. He’s had years of speech therapy, but in times of stress (especially stress involving Logan!), his control lapses and he reverts to old speech patterns.
I have slight residual R-W trouble myself (which can be inconvenient, considering my last name begins with R). When my sons were in fifth grade, they were friends with another set of twins, whose names were Wyatt and Riley (disclaimer: I didn’t choose my character’s name because of him!). I was never able to say those boys’ names in one sentence without thinking about it really hard.
Luckily, typing “Riley Morrel” is much easier than saying it—which is great for me, but not so much for my Stumptown hero. **Sigh** Poor Riley, the hapless victim of nefarious planning on the part of his creator.