In Alice's Adventures in Wonderland, the poet and mathematician Lewis Carroll tells a tale of a mouse's tail using a long-tail-shaped arrangement of words. Such a poem--which is offered in the shape of its subject--is called a concrete poem. A more general category is visual poetry--in which the shape of the poem in some general way relates to the meaning of the poem.
"Mine is a long and a sad tale!" said the Mouse, turning to Alice, and sighing.
"It is a long tail, certainly," said Alice, looking down with wonder at the Mouse's tail; "but why do you call it sad?" And she kept on puzzling about it while the Mouse was speaking, so that her idea of the tale was something like this :