I’m fairly certain of the why, at least part of it - stars have sharp points. But, is there another reason why stars weer commonly used, and still are?
And, most importantly, who started it? Wile E. Coyote getting bonked by an anvil in an early Ropad Runner cartoon? Dagwood losing a filling in one of his sandwiches in the 1930s (if they had him him eating like that back then.) Or what? And were they always used? Obviously WB has also used birds singing around the person/animal, but did those predate stars?
Finally, if there a set rule on white versus filled in stars, or is that up to the individual artist? Does one star always equal one unit of pain? In one Calvin and Hobbes comic he had been imagining himself as a loathsome fly, merrily spreading disease and filth everywhere, and at the end of this Sunday strip Hobbes asked what happened, & he says “I got swatted” - one star behind his bottom. But, in another one, he has a couple stars.