Why is yawning contagious and breaking wind not?!

Question:
I know my question sounds obsurd, but, there must be a good reason people start yawning when they see others yawn, but the same thing doesn't happen when they sense the air has been contaminated.
Answers:
I found a website that has why yawning is contagious, but not flagellating. Here it is

http://www.howstuffworks.com/question572.htm

Other Answers:
I just have to say. ewww. I am glad that breaking wind is not catchy.

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I dont want to sound crazy.. but just by reading the article left on that link above.. just in the 2 min that it took me to read it. i yawned like 4 times .. is impressive..
Answers:

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