The Cutter tool is used for breaking pitch blocks into sub-blocks so that the pitch can be tracked and modified more finely with respect to time. It is selected using the contextual menu or by pressing I on the computer keyboard. The cursor appears as a knife that can be applied (LEFT CLICK) at any point within a pitch block to break it. The vertical red line moves with the knife cursor to identify the exact position at which cuts will take place.
The result is two separate pitch blocks, each with a tracked pitch related only to that section of audio as shown.