2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/229607There are several physical situations in which the `tangling' of a loop is relevant: the game of cat's cradle is a simple example, but a more important application involves the stirring of a fluid by rods. Here we discuss how elementary topology constrains the types of mappings that can occur on a surface, for example when the surface is the domain of a two-dimensional fluid.7 pages, 5 figures, PDFLatex with RevTeX4. Published in Dynamical Systems Magazine (http://www.dynamicalsystems.org/ma/ma/display?item=292)Chaotic Dynamicstext