Cats purr.

Meaning: This means that cats make a soft, continuous, murmuring sound when they are happy or content. It's like saying, Cats make a soft sound to show that they are happy.

Choice of Words: Cats are small, carnivorous mammals that are often kept as pets. The verb purr means to make a continuous, soft, murmuring sound. When you put them together, "Cats purr" is a statement that describes the sound that cats make when they are content or happy.