There's a gag in Through the Looking-Glass chapter 3 ('Looking Glass Insects') that I don't think anybody has really got. Alice wanders into the forest where nothing has a name:
She was rambling on in this way when she reached the wood: it looked very cool and shady. 'Well, at any rate it's a great comfort,' she said as she stepped under the trees, 'after being so hot, to get into the — into what?' she went on, rather surprised at not being able to think of the word. 'I mean to get under the — under the — under this, you know!' putting her hand on the trunk of the tree. 'What does it call itself, I wonder? I do believe it's got no name — why, to be sure it hasn't!' She stood silent for a minute, thinking: then she suddenly began again. 'Then it really hashappened, after all! And how, who am I? I will remember, if I can! I'm determined to do it!' But being determined didn't help much, and all she could say, after a great deal of puzzling, was,'L, I know it begins with L!'Here's Hugh Haughton, in the Penguin Classics 'Centenary' edition (he is following Martin Gardner's explanation): 'L is for Liddell', which is the real Alice's surname. But this is surely not right: for when she recovers her name she does not call herself 'Liddell', but 'Alice.' No, the joke is otherwise. She is in a forest, but she cannot remember it is a forest. She meets a fawn, who cannot remember it is a fawn. When it leaves the forest it does remember ('I'm a Fawn!' it cried out in a voice of delight, 'and, dear me! you're a human child!' A sudden look of alarm came into its beautiful brown eyes').
No: 'I know it begins with L!' -- What begins with an 'l' is: lice. The joke is that for a moment she thinks she is a lice.