Well, more on sound – speech, to be precise – and its characteristics. Here, we have an example of incessant talking, with Charlie Brown making the mistake of asking Lucy for some chatter. He gets more than he bargained for, as denoted by a) the lack of space between the words in Lucy's speech balloons, indicating that she not only speaks very fast, but doesn't even seem to need to breathe in occasionally; b) the size of her speech balloons, completely dominating her panels. In fact, by having the second Lucy panel's balloon being larger than the first, almost crowding out even Lucy herself, Charles Schulz gives the reader the impression that far from tiring, Lucy is even stepping up her speed-talking effort. (This is of course reinforced by her not looking the least bit winded in either of the panels.)
Like I said previously; a master at his craft.