CARS to POOP.

Every letter change

1. CARS → CABS: change letter 3 from R to B.
2. CABS → COBS: change letter 2 from A to O.
3. COBS → COOS: change letter 3 from B to O.
4. COOS → COOP: change letter 4 from S to P.
5. COOP → POOP: change letter 1 from C to P.