Scott McCloud, the author of “Understanding Comics,” called the bubbles the graphic equivalent of quotation marks.
He said that the comics pioneer Will Eisner had called word balloons a “desperation device.”
Mr. Eisner was referring to the struggle to represent sound in a soundless medium.
Mr. McCloud added that bubbles created a consistent amount of negative space around words, which was desirable from a graphic standpoint.
The rounded edges of text bubbles also gave messages a soft, friendly connotation.
That’s an element especially useful in texted communication, where tone and body language are absent.
Mr. McCloud said that hard edges and right angles conveyed an unintended sharpness.
Ambiguity, especially in text messages and online, tends to be perceived negatively.