In A Wrinkle in Time, appearances are almost always deceiving – so it's what's inside that counts. For example, Charles Wallace looks like a normal five-year-old boy, but the way he thinks reveals him to be advanced beyond his years. Check out this exchange he has with Calvin when they first meet:
"What gives around here?" Calvin asked. "I was told you couldn't talk."
"Thinking I'm a moron gives people something to feel smug about," Charles Wallace said. "Why should I disillusion them?" (2.105-106)
Charles Wallace may appear to the public as a rather slow little boy, but his response to Calvin reveals that he not only is aware about what other people think about him, but that he's mature enough not to care, empathetic enough to understand their motivations, and wise enough to act accordingly. While you can never quite trust how a person looks in this book, pay attention to what (and how) they think, and that will tell you who they really are.
When Charles Wallace gives in to IT, it's not just his actions that clue Meg into the fact that something is deeply amiss – the very way he talks has changed.
The voice was Charles Wallace's voice, and yet it was different, too, somehow flattened out, almost as a voice might have sounded on the two-dimensional planet. (7.167)
Even if this robot version of Charles Wallace were saying the same things the real Charles Wallace always had, the way he was saying them would give him away regardless. The flatness of his voice, and the voices of the other Camazotzians, signals that something essential is missing that makes these people less than whole individuals.
Meals are social events, and the different food encounters our characters have tell us about the different groups of people they find themselves breaking bread (or unidentifiable alien food) with. Mrs. Murry's lab-cooked stew is simple and homely, but also shaped by her scientific obsessions; her willingness to share with unexpected guest Calvin shows her hospitality. The beasts' food isn't so appealing to look at, like the beasts themselves, but magically delicious; it suggests that the beasts are more than their appearance would suggest. And perhaps the most memorable meal in the book is the ill-famed turkey dinner on Camazotz. The fact that it tastes like sand to Charles Wallace shows how differently his brain works from Meg and Calvin's. And the fakeness of the turkey dinner encapsulates the hollowness of the entire Camazotzian society, and IT ITself. The proof is in the pudding, and in this book it's how the pudding really and truly tastes that counts.