Why does the fat lady's butt blow up in Babe Pig In The City?

The label the waiter guy pulls of her dungerees bottoms was stopping the inflation, after it was pulled off, her butt started to inflate because of she has such a huge bum, and it was free of it's confines, so it, when freed, started to inflate, tearing off her clothes and started to regain it's former shape. Either that of she just decided to become fatter.