It can anything but it's mostly the first word of a sentence for me. Once a get a bit of flow I'm not too bad but especially hard starting sounds like "t"s and " d"s. I find "h" starting sounds easier because it's easier to start the breath One of things some speech therapists recommend is to start talking halfway through an exhale to ease into hard start words. If you can practice that to a point where it's barely noticeable you might sound like a person who's had some speech therapy.