ACT — three cells with one turn
Trace ACT from row 1, column 1. Move down to row 2, column 1, then turn right to row 2, column 2. For a numbered check, follow 1 at row 1, column 1; 2 at row 2, column 1; 3 at row 2, column 2. The letters appear in the required A → C → T order.
This path makes one turn and forms two straight segments, spanning two rows and two columns. It records two edge visits and one corner visit. Its starting cell has one open orthogonal neighbor, while its ending cell has three. Completing ACT assigns the first three cells and leaves 16 open cells for the remaining words.