There may have been some mystery to the point of Post 188.8.131.52, for those members of the wide world who do not know how funny my father thought farts were. He thought they were hilarious.
He bragged about having taught my mother to fart with family members present, laughing at the idea of holding it in when in one's own home. He rated noises.
Somewhere along the line, he started calling them bee-oops. I think it started with a fart story that he told, during which he described the noise (beeeee-oooop) to enliven the experience. I don't think he ever said the word without grinning.
Since beans were known to, shall we say, provide ammunition for the fart wars, it was a small mental leap to begin to refer to them as farts. The whole family had used the word to mean farts for about a year when my sister and I went to camp. The thing that happened while we were at camp was the shift from effect to cause.