Ohhh - sorry, it's only just occurred to me - you never umm when you're nervous, do you?
You see, a lot of humans do. In public speaking, in meetings, in the pub or meeting people unexpectedly on the street.
The brain hears a question and is on a go-slow, either too little coffee, too much coffee, too much stimulus or churning bigger questions, like why the hell did I wear this shirt and how am I gonna hide that massive grease stain and damn I wish I had a spare jumper in my "Oh, hi -- umm - uhyeah, no, it's umm... it's, well, it's umm going well thanks -- yes I am, thank you -- yeah, it's only been oh, umm, a month, umm... oh three months actually -- umm, yeah, she's umm, no I mean sure, she's not the, umm, I mean she's got, umm, a lovely"
(And then the car-crash of a conversation ends with them pointing to your starbucks cup and saying "Anyway, I gotta go - enjoy your coffee!" and you shout back "Yeah, you too" then realise they haven't got any kind of drink in their hands but at that point you really don't want to care, you just want to be walking. Away.)
Because in situations where the brain feels rushed, the brain tells itself "YOU NEED TO ANSWER NOW" and so, without any training otherwise, usually says umm or other filler rubbish in the (not-so-conscious) hopes that the other person won't realise that you're frantically scrabbling to find real content and coming up woefully short. And the real content that does come up, if it does come up, arrives in the most unhelpful way, and you end up saying horrible things and wish you'd just stuck with "umm".
Even in a presentation, where you've practised a million times and your cat is frankly bored of hearing about your financial projections for the 15th time in a row, but you get in that room and you see the slide and you realise it doesn't tell you as much as it told you when you wrote it, your mind fills with.... "ohhhh... I know this.... this was the one, about.... ohhhhhh....." and your mouth says "Right. Umm... so we, uhhh, on this one, ummm, so as you may be aware, well some of you.... ummm..."
Maybe some people's hesitations aren’t communication failures but successes. But some hesitations are not about truth. And often they compound themselves, making more little hesitation babies as you hate yourself a little more for the unintended hesitation that sounded meaningful that just passed out of you.
And maybe the answer is stupidly simple: Cut yourself some slack. Allow pauses. Learn to ride the awkward silence. Learn to laugh at yourself under pressure and practice witty things to say to replace the filler.
But that's not as easy as, well now you have the answer so what's the problem. That actually boils down to "retrain every neuron in the linguistic centres of your brain that have been growing since the age of 6"
That takes some practice, and as annoyed as your cat may be that it's having to listen to yet another presentation, it can't replace the pressure of real life. Hence, I guess, a tool that helps you measure your progress in real life.
Because sometimes "your goal" is just to get through one day without feeling like an absolute muppet.