Where the red fern grows shatter 8 how did grandpa get the idea for his trap

Billy tries to trap a coon so he can train his dogs with a coonskin, but the coons prove too wily. His Grandpa teaches him to catch a coon with a simple brace and bit, and a shiny piece of tin for bait. Although the coon merely has to let go of the object to free itself from the trap, coons stubbornly hold onto objects. Grandpa learned this trap as a boy.