What's Inside A Catfish?

Huck and Jim caught a catfish as big as a man; to be precise six feet two inches. It could of pulled them into the Illinois. They sat there and watched it drown, and then they cut it open. There was a ball in the catfish’s stomach. They cut it with a hatchet. Inside the ball there was a spool. Jim said it had been there a long time. Now, why would a catfish swallow a spool?