Hansel (red=1) and Gretel (blue=4) walk through a forest, leaving a trail of breadcrumbs (yellow=7) behind them. A witch (grey=5) lurks near a candy house (value=9). In the masked grid, birds have eaten the breadcrumbs — all the 7s along the path become 0. The children have reached the witch's house. Without the trail, they cannot find their way back.