"It's a little tiresome to walk backward, but that is the only way to pass this part of the road, which has a trick of sliding back and carrying with it anyone who is walking upon it." With new courage and energy they now trudged forward and after a time came to a place where the road cut through a low hill, leaving high banks on either side of it.

They were traveling along this cut, talking together, when the Shaggy Man seized Scraps with one arm and Ojo with another and shouted: "Stop!" "What's wrong now ?" asked the Patchwork Girl.
"See there!" answered the Shaggy Man, pointing with his finger.
Directly in the center of the road lay a motionless object that bristled all over with sharp quills, which resembled arrows.

The body was as big as a ten-bushel-basket, but the projecting quills made it appear to be four times bigger.
"Well, what of it ?" asked Scraps.
"That is Chiss, who causes a lot of trouble along this road," was the reply.
"Chiss! What is Chiss?
"I think it is merely an overgrown porcupine, but here in Oz they consider Chiss an evil spirit.

He's different from a reg'lar porcupine, because he can throw his quills in any direction, which an American porcupine cannot do.

That's what makes old Chiss so dangerous.