PAID to POOP.

Every letter change

1. PAID → PAIL: change letter 4 from D to L.
2. PAIL → PALL: change letter 3 from I to L.
3. PALL → POLL: change letter 2 from A to O.
4. POLL → POOL: change letter 3 from L to O.
5. POOL → POOP: change letter 4 from L to P.