Charlie Brown began as kind of a smart-aleck. We know his destination is to be a kind of downcast everyman. Here's a bit of a transitional state, that of being kind of paranoid about what others think about him.
I image Snoopy moving here in much the same way that snakes do. It's a fun illustration.
In the first of these strips, Lucy doesn't have a good sense of relative distances. In the second, she's gotten the distance down but wonders, if Mars is so far away, why she should care. Lucy is the type of person who can make a leap from ignorance directly to dismissal.
More Pig-Pen strips. Not being bothered by girls is a questionable virtue. I can see the mosquito thing, but I'd think the presence of other vermin might make up for it.
Although Schulz returns to Pig-Pen periodically throughout Peanuts' run, it's without any great fervor. Jan in comments a few days ago remarked that, in all of Peanuts, there are only around 140 Pig-Pen strips. We've now seen ten of them.
While there's something admirable about Pig-Pen's lack of self-consciousness, as that prior commenter said, there's not a lot you can say about him. I think Schulz returns to him every once in a while because A. he's kind of a link to the early days of Peanuts, and B. it's a character quirk that never needed updating.
Peanuts lasted up to the dawning days of the 21st century, and throughout that time some updates to the cast were necessary. Lucy changed her dark blue dress for a track suit. Eudora's clothes would have been unthinkable in 1951. Need I even remind you of Franklin? Snoopy's typewriter was out of date at least a decade before he wrote that final letter.
There have always been, and probably always will be, messy kids, so Pig-Pen never needed revising or replacing.
It's funny to think of a dog as being afraid of getting his mouth dirty. Most dogs I've known haven't been what I'd call discriminating eaters.