The four-letter path
Trace PLUM from row 6, column 2 and move right three times. Follow these cells in order: 1 at row 6, column 2; 2 at row 6, column 3; 3 at row 6, column 4; 4 at row 6, column 5. The letters therefore read P → L → U → M without any change of direction.
All four cells form one straight segment spanning one row and four columns. The route makes four edge visits and no corner visits. Its starting cell has two open orthogonal neighbors on the raw board, while its ending cell has three. Once these four cells are accounted for, 26 open cells remain.