Difference between Yawning and Sighing?

Yawning is a forced inhalation to take in more oxygen when your body has too much carbon dioxide. Sighing is an exhalation which serves more a psychological purpose in expressing your emotions. However since you are exhaling it is followed by a little more inhalation which makes a small rise in body oxygen.

BTW Jon, has anyone carefully looked at that fun fact about casinos pumping in oxygen? If you look at the volume of air in a casino (340000 sq ft of 20 ft high casino space at Foxwoods) it is hard to believe that there is that much bottled oxygen to waste. Also has anyone every seen a huge oxygen tank in back of a casino? Have you every seen a oxygen delivery tank truck stopping at a casino? I think that is just a fantasy invented by a loser trying to explain to his family why he had to give the casino the deed to his house : "The oxygen made me do it."

Well, yes they serve the same purpose, but for different reasons. Yawning usually happens as a result of lack of oxygen because of exhaustion or something like that. Sighing happens when you are frustrated or upset, and usually serves to calm you down, not because you are lacking oxygen. Pure oxygen causes your brain to release chemicals and hormones that calm you down, which is probably why you take a deep breath to get more when you are upset.

So I don't think sighing is contagious, and yawning hasn't been proven why it is "contagious", although most people seem to think its behavioral.

Interesting side note: Casino's pump in more oxygen into their rooms than normal, in the hopes that this will cause gamblers to stay calmer, meaning they are more likely to continue playing even if they are losing. Fun Fact.

[Edit] In response to Rich Z:

There's a couple books out there on Casino design, "Designing Casinos to Dominate The Competition" is one of them, where they state this. They also state other things which are observably true, how there are no clocks so you don't keep track of time, how it's like a maze to keep you looking around, how the rugs are boring so you look at machines, the constant ringing of bells to make you think people are winning, no windows for distraction or to prevent the weather from affecting your mood, slot machines that pay out more often at the entrances to draw you in..... the list goes on and on.

And no you don't see the trucks but you don't see a lot of the backscenes of casinos, so I don't doubt it. I'm not saying the air is pure oxygen, but I wouldn't doubt it if some casino's pumped a little extra in the ventilation.

you yawn when you're sleepy. you sigh when you're bored. yep. same purpose. nope. not contagious.