This is a hands-on demonstration. Try this with your friends, and be prepared to explain the physics of the demonstration to them. When the wire applies sufficient pressure to the open structure of ice, it crushes the ice to the liquid phase, i.e., it melts the ice. After the wire passes through the liquid, the water water above it refreezes now that it is no longer under pressure. Thus, the block doesn’t separate into two pieces.
Work Step by Step
This is discussed on page 328, and Figure 17.16.