Why do cats yawn?

Why exactly do we—cats, humans, and other species—yawn? Why, without thinking about it, do we fully open our mouths, partly close our eyes, take a deep breath, and then exhale? 

Yawning is considered an involuntarily action. That is, the one yawning cannot help but yawn. What about cats? Why are they yawning? 

One of the reason could be that because it's contagious! Why not? It is for us human! There is scientific proof that if you see someone yawning, you may soon start doing it yourself; I'm sure you are yawning as you read this sentence. Yawning is contagious. There is also a study that shows that human yawns are contagious for dogs. While I did not find similar research done on cats, I cannot think of a reason why cats would be different.