When a wound on the skin creates a gap, the epithelial cells of the skin, surrounding the wound, move in a concerted fashion to close this gap. The boundaries of these gaps can have different curvatures; they could either be convex or concave. Interestingly, the cells situated on the convex-shaped surfaces form large membranous outgrowths and crawl towards the empty space; while on a concave surface, the layer of cells contracts together, tugging at the margins of the wound and gradually closing the gap.