On the surface, the Caterpillar states a binary rule: different parts of the mushroom produce opposite effects. The instruction is deliberately minimal—no guidance on which side is which or how much to eat—forcing Alice into trial-and-error. This is the point. The line reframes Wonderland’s unruly transformations as manipulable variables. Instead of passively suffering cakes and bottles, Alice acquires a tool that requires method: bite, observe, adjust. The mushroom’s ambiguous “sides” (on a perfectly round cap) introduce a paradox that pushes Alice toward practical rather than theoretical knowledge. She learns to define “sides” by results, not appearance. The line also advances the identity question raised moments earlier (“Who are you?”). If size shifts scramble self-perception, experimental control becomes a means of self-stabilization: by learning what makes her taller or shorter, Alice can approximate a desired self-presentation, whether to approach a tiny house or to reach a key. Finally, the sentence foreshadows the rest of the chapter: Alice’s exaggerated neck and the Pigeon’s misidentification dramatize how partial control invites new problems, yet the iterative process ultimately restores a functional “usual” size and a steadier confidence.