Passing Gas.

Before you read what I have to say, allow me to explain where it all stemmed from. Today I observed the following situation take place.
Quinn and Avery were about to get into the tub, but prior to doing so Quinn "passed" a little somethin' somethin'. What followed was the scene of the two of them laughing hysterically about the whole thing.
That gots me to thinking...

What I have to say is of no great importance, in fact, if I had any class I wouldn't even be bringing up the topic. But, inquiring minds want to know.
What makes passing gas so funny?
Not so much funny to me (although I have been caught off guard by the occasional squeaker and broken a smile, I must admit) but rather to my little dears (even my innocent two year gets in on "the act". In fact I have witnessed the little dear entertain himself by "forcing" a toot, then laugh about it, only to reapeat the processs over and over again).
Seriously, what is it? Is it the honking sound that's produced? Could it have something to do with the body part from whence the honk originated? Surely it is not the odor.
Nevertheless, nothing seems to trigger a bigger smile or deeper laugh out of my little ones than production of an air biscuit.
What's more, it doesn't necessarily have to be the actutal creation of a ripper-rooni. For example songs about the deed..."beans beans the magical fruit"...and the ever popualar arm fart get almost as big a reaction as the real deal.
I cannot understand it. Truly it really is not that funny and yet we have all found ourselves giggling about it at one time or another.
Apparently my small mind will never be able to explain this phenomenon. IT IS the eighth world wonder to me.