Ferrofluids are liquids that exhibit magnetic properties at room temperature, consisting of tiny magnetic particles suspended in a carrier fluid. They are known for their unique behavior in magnetic fields, forming spiky shapes that visually demonstrate magnetic field lines. While ferrofluids can stain surfaces and are difficult to remove, they maintain their constituents without significant separation due to the nanoscale size of the particles, which are influenced by Brownian motion. Other liquids like mercury and liquid oxygen do not possess magnetic attraction, making ferrofluids the primary example of a liquid that meets the criteria of being magnetically responsive without separation of components.