Researchers used computer modeling to show how cells can feel their way through their surroundings, important when, for example, a tumor cell invades a new tissue or organ. This computer simulation depicts collagen fibers that make up the extracellular matrix in which cells live. Local arrangements of these fibers are extremely variable in their flexibility, with some fibers (blue) responding strongly to the cell and others (red) responding hardly at all. The surprising amount of variability in a local area