Yeah, the pig preserves the horizontal line across the panels and mirrors the previous word balloons. From a composition standpoint, I think It’s a smart choice.
I wonder what Ernie would say. Probably, “I drew what I thought looked good.”
I buy the notion that the gag doesn’t need explaining, but I wonder if the pig doesn’t help fill the panel and make it more visually interesting. (I tend to find Bushmiller’s cartooning from this era impeccable, even when the jokes don’t land very hard.)
The contrast in the last panel is beautiful cartooning.