This is Animal Vegetable Mineral Abstract. Pigs are actually hatched from eggs. Farmers keep this secret because they have nothing better to do with their time than that sort of thing.
Rap music was never intended to be a genuine musical genre. It was created, partly as a joke, partly as an experiment by some geeky Cambridge students in the 60's on the grounds it was ironic - they modelled it deliberately to be music that could never possibly "catch on".