What does the Caterpillar give Alice to help her change size?

The Caterpillar gives Alice a piece of mushroom to help her change size.

In Chapter 5 of Alice’s Adventures in Wonderland, the Caterpillar explains that one side of the mushroom will make Alice grow taller and the other will make her grow shorter. Alice breaks off pieces from both edges because the mushroom is round and she cannot initially tell which side does what.

This scene follows several earlier size changes caused by bottles, cakes, and Alice’s attempts to reach a garden. The mushroom is therefore not a potion or a cake, although those objects also affect her size elsewhere in the story. The Caterpillar does not hand her a prepared object; he tells her how to use the mushroom, and Alice breaks off the pieces herself.

The episode is one of Carroll’s best-known examples of Wonderland’s playful, nonsensical logic: a perfectly round mushroom has two meaningful “sides,” and Alice must experiment to discover their effects.