People have long noticed that the cat's eyes glow indarkness. Because of this, these animals were attributed to magical properties. It was believed that cats are favorite animals of witches, hence the fear of a black cat.
However, there is no mysticism in this. The answer to the question, why the cats have glowing eyes, will be understandable if you learn the features of cat sight and lifestyle.
The fact is that cats are nocturnal animals. Once, when they were not domestic, cats hunted small animals at dusk or at night. And for this they needed sharp night vision. On the inside surface of the cat's eye there is a special reflective layer - tapetum. Thanks to him, cats can see perfectly in the dark. Tapetum reflects even a weak light source, but if the cat is planted in a completely dark room, then her eyes will not glow; they will have nothing to reflect.
More on how to see cats, you can read in articles How do cats see and Why does a cat look into the eyes.