The four-cell vertical route
Trace HOOK from row 1, column 3 straight downward to row 4, column 3. You pass row 2, column 3 and row 3, column 3 without turning, so the route forms one straight segment across four rows and stays within a single column.
Read the four cells as 1 at row 1, column 3; 2 at row 2, column 3; 3 at row 3, column 3; 4 at row 4, column 3. They spell H → O → O → K. Both endpoints have two open orthogonal neighbors.