If your kitty goes gonzo for catnip (half of all cats do), treat them with a small, handmade toy to hold their stash. Scientists agree that smelling, rather than eating, catnip garners the biggest response but they still aren't sure what neurological reaction catnip triggers for sensitive cats. It's thought that it stimulates receptors in their brains that makes them feel initially energetic, playful and happy, then mellow and relaxed. Stitch up your own with our step-by-step instructions.