Sure, we don't really see any of the boys at Camp Green Lake interact with their families. But the characters' relationships with and attitudes toward their family members are super important clues to what those characters are like. The gentler, more vulnerable boys tend to care deeply about their family relationships. Stanley, of course, writes to his mother regularly, and enjoys reading the letters she sends in return. While Zero doesn't know where his mother is, it's clear that his relationship with her was a close one, and that he misses her badly.
The tougher, less sympathetic characters in the book, on the other hand, never mention their families. Some of the boys actually make fun of Stanley for his devotion to his mother. That makes it especially significant when Squid – toward the end of the book – asks Stanley to call and deliver a message to his mom. It's kind of a sign that all of the boys, not just Stanley and Zero, might have been changed a bit by their stay at Camp Green Lake.
Most of the characters in Holes have more than one name: think "Stanley" and "Caveman." Which names are used, when, and by whom, can give us some pretty important inside info about a character's personality or attitudes, as well as their place in the hierarchy of the camp.
For instance, Mr. Pendanski insists on calling the campers by the names that "society will recognize them by" (5.30) – that is, their given names. But the boys prefer to call themselves by the nicknames they've assumed since coming to camp. In one way this is a nod to X-Ray's power – he's the one who assigns the nicknames. But it's also a way for the boys themselves to claim some control over their own identities. Your name, after all, is usually one of the first things people learn about you, and calling yourself "Armpit" as opposed to "Theodore" definitely give us a more, um, casual identity.
Other names give us even more direct information about the inner life or situation of a character. "Miss Katherine" sounds very much like a respectable, sweet-natured schoolteacher, while "Kissin' Kate" is clearly a name suitable for an outlaw.
Because each name gives us quick way to understand and access the type of character we're dealing with, it's interesting that we're never given any name for the Warden other than her institutional title. Does this affect how we think of her, or what kind of sympathy we're capable of feeling toward her?
And what do the other names in the story tell us about the characters? Think about Stanley Yelnats, whose name is spelled the same forward and backward. Or, of course, Zero. Can't forget about the little guy.
Not all habits are either good or bad. Some are just plain… habitual. In Holes, characters are often defined by little mannerisms and repeated behaviors. Stanley has a tendency to shrug a lot, which is a good indication of how unwilling he is to take a position on things. Most often, in fact, he only shrugs with one shoulder – even his shrugs are half-hearted.
Mr. Sir, of course, is constantly eating his sunflower seeds and spitting the shells out everywhere, which clues us in to the fact that he's not exactly the type of character we want to take with us when we have tea with the queen.
Sometimes characters have habitual ways of speaking, like the Warden with her softly menacing "Excuse me?" Her habit of using this phrase to intimidate anyone who challenges her lets us know pretty handily that she's used to having her way; oh, and that she's dangerous. Zero, on the other hand, has more of a habit of not speaking; after the umpteenth time of being told "Zero said nothing," we might begin to wonder what's going on. In fact, Zero's consistent silence in the face of questions and verbal assaults is our first indication that there's probably more to him than meets the eye – or maybe we should say, the ear.