The study probably controlled for this, but not mentioned in the article: um&#x27;s give listeners time to think.<p>Corollary: removing disfluencies from online lectures diminishes comprehension.<p>I took Ullman&#x27;s &quot;Automata&quot; course, and they&#x27;d edited out all the um&#x27;s and pauses etc in the vidoes, making them half as long. It reduces download size, but made them really difficult to understand. You don&#x27;t have time to process  one interesting thought before the next is upon you. Very different from live lectures. I often had to rewind 5 to 10 times.<p>Yes, the material isn&#x27;t easy and Ullman is full of insights, but this happened even with the beginning of the introductory lecture.<p>From this article, it seems that the um&#x27;s and pauses would also have helped signal difficult vs easy ideas. (Sometimes I worked hard to grasp his precise meaning, only to realize he was speaking casually).