WHAT to POOP.

Every letter change

1. WHAT → CHAT: change letter 1 from W to C.
2. CHAT → CHAP: change letter 4 from T to P.
3. CHAP → CHOP: change letter 3 from A to O.
4. CHOP → COOP: change letter 2 from H to O.
5. COOP → POOP: change letter 1 from C to P.