Anicca: Impermanence
Gold and silver, thought to last forever, are already cankered and eaten through with rust. Even the hardest metal is quietly rotting in the vault. Coins left in a damp chest, green and pitted when the lid is finally lifted.
Ādīnava: The danger in things
The rust becomes a witness and then burns the flesh like fire, showing the hidden hook inside hoarded wealth. What promised safety turns and bites the one who clutched it. A snake kept warm in the shirt for its bright scales.
Macchariya: Miserliness
Heaping treasure together is the grip that piles and piles and never opens for another's need. The hoard corrodes precisely because it is only hoarded. Grain locked in the barn while it molds, feeding no one.
Kamma: Action and its fruit
The fire that eats the flesh ripens from the heaping itself, the deed returning home to its doer. The rust on the coins is the rust the grasping earned. Bank a fire in the chest and it will burn the one who banked it.