Analysis of two chimpanzees' conversations with their teacher during a tool-use training task demonstrated that chimps use lexigrams, a humanly devised visual symbol system, selectively to encode perceived variability. (They generally use the symbols todifferentiate alternative possibilities or to represent change or novelty, leaving unsaid what is unchanging, repetitive, or the unique possibility in a situation.) The same phenomenon can be observed in children's language use in the one-word stage.