Why doesn't Snap get smudged by Rudy when he touches him? Or anything else in Chalk Zone, for that matter?
Yeah, but magic chalk has all the vulnerabilities of regular chalk, so it seems weird that this one is excused for unexplained reasons.
Isn't the reason they're usually in Chalk Zone?
It's possible that zoners and inanimate things in ChalkZone take on at least some of the properties of what they are supposed to be, and thus can no longer be smudged as that weakness of chalk is overridden by the new properties given to it. For instance, the reason Snap isn't smudged is because, although he's chalk, his skin is of the same toughness as human skin while his clothes don't smear because they share the same properties as their Real World counterpart, just with the whole being made of chalk added in the mix.