Ski resorts invest a lot of time and money in grooming. A perfect piste (finish) with the characteristic grooves contributes significantly to the skiing pleasure the next morning. However, if the slope is skied during the night, the tracks freeze solid. Just as streetcar tracks are problematic for cyclists, frozen ski tracks can become dangerous, especially for narrow children's skis. The problem occurs especially in late winter, when the snow is soft in the evening and then freezes through on starry nights.