CARD to POOP.

Every letter change

1. CARD → CARP: change letter 4 from D to P.
2. CARP → CAMP: change letter 3 from R to M.
3. CAMP → COMP: change letter 2 from A to O.
4. COMP → COOP: change letter 3 from M to O.
5. COOP → POOP: change letter 1 from C to P.