de Leeuw, Esther. "Hesitation Markers in English, German, and Dutch." Pp. 85–114.Very engaging piece, treating the phonetics of these little creatures (vocalic versus vocalic-nasal, etc.) and where they appear (with regard to pauses or silence, before or after utterances, etc.). She finds significant differences among the languages studied, with lots of inter-speaker variation, as you'd expect.
But what lucky timing ... today was of course the day that Sara Taylor, former White House political director, was supposed to testify before the Senate. In addition to saying that her boss won't let her say anything, she stumbles around a lot and uses striking quantities of hesitation markers. In the video below, there's a fair bit of it, like around 1:51.
The thing is aggravated by the creaky quality of her voice. (I'm listening with low-quality sound here, but I think that's what's going on.) And you've got to be sweating bullets under those circumstances, knowing that this could be bigger than Watergate and all that, with an attorney at your elbow telling you when not to talk, knowing that whatever happens, it's highly unlikely to end well for you, and so on. But man, this is some hesitating.