WDCS160 'The Christmas Camel', page 4

Speech Balloon (also known as Word Balloon and Speech Bubble) is the term for the limited space in the story's panels where the drawn characters speech and thoughts appear. Barks was a master of not only creating dialogue for his characters, but also placing the dialogue in inventive and interesting speech balloons that strengthened the reader's understanding of what was happening in the story.
Basically, a speech balloon is text in a white, fluffy looking area that in some way resembles a normal cloud. The balloon is usually found in the upper half of the panel. The balloon is always adjusted to fit the other graphic elements in the panel.

In several stories Barks had concrete difficulties placing the balloons, because some of the secondary characters towered upwards in the panels' natural balloon spaces. This was recurrently true when he drew the tall primary character Gyro Gearloose alongside the smaller ducks. Barks often expressed his vexation that he had made Gyro twice as tall as the other primary characters; one result of this decision was the very real difficulty of placing the balloons in unconstrained and convincing ways.
Here is another example, where a camel towers up in the panels. It is easy to see that Barks had difficulty 'forming' the large animal to fit the panels with the necessary balloons - and without leaving the Ducks as tiny specks in the panels.