TRAY to POOP.

Every letter change

1. TRAY → CRAY: change letter 1 from T to C.
2. CRAY → CRAP: change letter 4 from Y to P.
3. CRAP → CROP: change letter 3 from A to O.
4. CROP → COOP: change letter 2 from R to O.
5. COOP → POOP: change letter 1 from C to P.