Running can relieve anxiety and stress, allowing them to play with the mouse. The ball diameter is approximately 3.94cm, suitable for hamsters, small hedgehogs, and other small pets. Removable pillowcase, no need to worry about small pets dropping it. Easy, we offer 4 colors: blue, red, yellow, and.. Toxic but safe. Easy and convenient to assemble, it's a great toy for playing with mice and exercising. Reinforced structure, not easily broken. Multiple ventilation holes provide good airflow.