Your cat is chasing its tail because it does not realize its attached to itself. Cats are not always the brightest creatures, this behavior demonstrates just how clueless they can be. Your cat is full of energy and wants to play all the time, this is especially true for kittens. This desire to play with whatever is at hand explains why a cat would be enthralled with its own tail. A cats tail never stops moving until the cat gets sick of chasing it, the same can not be said for the human who tires of throwing a string around for their cat. Your cat is obviously aching for more quality play time, we recommend giving more attention to your cat. We all need to protect our cats from themselves and try to end this tail chasing madness before a cat loses a tail!
It is also quite common for cats to chase laser lights.