I have a very quiet internal monologue and when i think it’s not actually in my voice, it’s in somebody else’s voice. I don’t know who’s but if i had to guess, probably someone from an anime or cartoon since that’s mainly what i watch. So in terms of thinking, i don’t stutter since it’s not my actual voice. I don’t have any trouble with chewing yawning or blowing a bubble or anything like that ! If it helps, i can feel when i’m about to stutter though, it’s like a feeling under my tongue and my jaw kind of. I just tried the little smiling exercise and funny enough, i stuttered more. I couldn’t get past the first two steps haha