Dogs are colour-blind (色盲的)
Dogs are man's good friend. Some dogs are big, and some dogs are small. Dogs are very clever, but they cannot see colours. They are colour-blind. In a dog's eyes, everything is black, white and grey. How can a dog hunt (捕猎) for food then? Dogs can run very fast. They can hear and smell very well too. Many animals cannot see colours, Lions, tigers, cats, cows and sheep are all colour-blind. But monkeys can see colours. Many birds, fish and insects con see colours too.