This interactive tree chart displays a hierarchical animal classification diagram, with categories like Animal, Reptile, Mammal, and their subcategories. Users can click nodes to collapse or expand branches, with smooth 750-millisecond transitions animating the layout changes. The visualization uses D3.js version 3.5.17, specifically the `d3.layout.tree` and `d3.svg.diagonal` APIs to compute the node positions and draw curved links. Node circles are styled cyan with black borders, links are red, and the page background is pink, all defined through CSS within the embedded HTML file.