NaillyCat-eye is gel polish containing microscopic magnetic particles. While the colour is still wet, the tech hovers a magnet over the nail; the particles rush toward it and are frozen in place when the gel cures, forming a soft band of light that appears to slide across the nail as your hand tilts — like the eye of the gemstone it is named for.
The effect is strongest over dark, rich bases — emerald, sapphire, oxblood — and the magnet pass is a genuine skill: the stripe can run straight, diagonal, or radiate from a point. Cat-eye requires specific magnetic gels, so it lives in some artists' kits and not others — worth confirming before you book, which is exactly the kind of question Nailly's artist kit answers up front.