For me it’s “hard sounding” letters. Hard C (car, cat, etc), hard B (bill, boat), hard G (golf, gate), hard M (mother, moat). If the word has a blending first syllable I’m fine: CLoud, FLute, BLanket etc. But yes I def know in advance what words I’ll get stuck on so I change them mid-sentence to another word that has the same meaning. Instead of saying “It’s cold outside” (i know i’ll stutter on COLD). Instead I’ll say “It’s freezing outside”. Different word, but the same meaning to whoever I’m talking to.