A comment written by C K Dexter Haven on this site, The Straight Dope.The only cartoonist (to my knowledge) who actually made fun of the speech balloons was Walt Kelly.
At various times in POGO, Kelly pulled tricks like:
- People puncturing the balloon and letting the letters drip out
- An insect (bee?) getting caught in a balloon and unable to fly out
- One character thinking of a picture-image (such as an ice cream soda) and another character reaching into the thought balloon to grab it
- One panel with a character giving a long speech, and the other character cramped in the bottom corner of the panel, muttering about how the balloon took up all the space
- The most complicated: one character had trained fleas to spell out words, and was trying to sell this idea. You don't need to talk, the fleas will talk for you. (This ultimately led to a punchline where one character was complaining of spots before his eyes.)