- "Dad. I'm gonna leave this apple here. The core might be hard, but... The core... The core might be too hard to eat, but be SURE you eat it!"
- — Claus
The Nail File is a key item in Mother 3. After Flint wakes up in jail in Chapter 1, Claus eventually enters, telling his father that Lucas is still at his Hinawa's grave. He gives his father an apple, repeatedly mentioning its core. After Claus leaves the jail, Flint can eat the apple, eventually biting down on (and finding) the Nail File. Flint uses it to break the cell door's rusty lock, making it unusable and removing it from his key items in the process.