I believe it is standard practice to use a margin which is puffed out when expressing a cartoon character's thought instead of speech. I recommend Nick Piekos' recommendations: http://www.blambot.com/articles_grammar.shtml
思想泡泡混音
cartooning、Reimagine、remix+257786、thought
漫畫、重新構想、混音+ 257786、思想
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