For the longest time, and still currently, it was any word that had a “Sk” sound at the beginning. School, scratch, scare, etc. I’m 44 and just this past year, I’ve had issues with words that fall completely outside of my “trouble” words. Sometimes it surprises me on what words I’ll stutter on and I literally laugh at it now. I’ve come to terms that I’ll always have the random stutter and I don’t let it get the best of me. For reference, I consider my stutter to be mild but it can get bad on certain days. In my case, I think it’s all my current mental state as I can have moments of completely stutter-free moments that can last hours , so I know , for me, it’s mostly all mental and possibly also physical. If I breathe and relax then I’m ok. If I get anxious, it affects my breathing and seems to trigger my muscle control.