It tends to be through conversation with them and interaction with them. You see how the speak to others, as well as about themselves, and also observe the ways they interact with the world around them.
Comic strips work in a similar way.
Since cartoons only used the sings essential to establishing meaning, words can be used to further explain what is going on in the panel. For example, in this Peanuts cartoon, dialogue is used to explain why only a white silhouette of Snoopy's doghouse and sleeping figure are depicted. Mr. Boffo's dog, for example, could be a number of things. This sort of understanding is dependent on the anchoring text establishing itself inside the meanings used in the narrow-cast code that is common to readers of the specific cartoon. Anchoring text serves the purpose of defining a cartoon's identity as well as the identity of their environment.