Read the excerpt:
"There's not a single lump here!" she said at last. "There's not a lump as big as a pin - except backbone lumps, and you can only feel them because you're thin. I've got backbone lumps myself, and they used to stick out as much as yours do, until I began to get fatter, and I am not fat enough yet to hide them."
What is the meaning of the figurative language "a lump as big as a pin" in the excerpt?

It's hardly noticeable.

It is sharp.

It sticks out like a point.

It's invisible.