After a minute or two, they began moving about again, and Alice heard the Rabbit say, “A barrowful will do, to begin with.”
“A barrowful of what?” thought Alice. But she had not long to doubt, for the next moment a shower of little pebbles came rattling in at the window, and some of them hit her in the face. “I’ll put a stop to this,” she said to herself, and shouted out, “You'd better not do that again!” which produced another dead silence.
Alice noticed, with some surprise, that the pebbles were all turning into little cakes as they lay on the floor, and a bright idea came into her head. “If I eat one of these cakes,” she thought, “it’s sure to make some change in my size; and, as it ca’n’t possibly make me larger, it must make me smaller, I suppose.”
So she swallowed one of the cakes, and was delighted to find that she began shrinking directly. As soon as she was small enough to get through the door, she ran out of the house, and found quite a crowd of little animals and birds waiting outside.

Alice's Adventures in Wonderland, Chapter 4 - The Rabbit Sends in a Little Bill