HORN: down once, then across the bottom
For HORN, select H at row 4, column 1, then O at row 5, column 1. Turn right to R at row 5, column 2, and continue right to N at row 5, column 3. Reading those four positions in order gives H, O, R, N. Keep the downward opening separate from the two rightward moves: the direction changes after the second letter, and the final three letters share a row.
The route uses two straight segments and makes one turn. It spans two rows and three columns, and all four selected cells lie on the board's edge, including one corner. That gives you a visual cross-check beyond the spelling: the path follows the outside rather than cutting through the interior. Once these four distinct cells are accounted for, 18 open cells remain. Leave this route at four letters when you move on to the five-letter slot.