"I have a little shadow that goes in and out with me,
and what can be the use of him is more than i can see.
he is very, very like me from the heels up to the head;
and i see him jump before me, when i jump into my bed.
the funniest thing about him is the way he likes to grow—
not at all like proper children, which is always very slow;
for he sometimes shoots up taller like an india-rubber ball,
and he sometimes goes so little that there’s none of him at all.
Robert Louis Stevenson, A child’s garden of verses