Cat vision isn’t as clear as ours. Because they are true predators, their vision is designed to pick up quick movements of prey, especially in dim light. Cats and dogs have more rod cells that can quickly refresh to pick up the slightest movement of prey walking through the grass at dusk. They have fewer cones which are responsible for our detailed and sharp color vision.
Feline vision is blurry, but their peripheral vision is much better and has more range than ours, enabling them to see a mouse out of the corner of their eye. The smallest movements capture a cat’s attention, and if it shines that’s a reason to investigate.
Cats focus on shiny objects for the same reason we do – curiosity. If you spot something shiny on the ground, your impulse is to investigate. It gets your attention because it might be something special, like a lost ring or coin. Perhaps it’s nothing more than a piece of glass or tin reflecting sunlight. It doesn’t matter what it is, we check it out because it’s shiny. Curiosity may grab a cat’s attention too, but the main reason they steal our shiny things is for attention and wanting to play.