A thin NITINOL wire loop is connected around two pulleys. The lower pulley is placed half way into the water at 35-40 degrees celcius and an ice cube gently touched to the wire. If the wire is gently spun downward through the ice cube into the water bath, it will continue to spin, cutting the ice cube in two.
Alternatively, a glob of crushed ice placed around the wire as it enters the box will cause the wire to circulate as described above, as shown in the photograph.