JOKE: A young boy and his mother are traveling

A young boy and his mother are traveling across the state by train to see his aunt. While waiting in line to purchase tickets, the young fellow starts sucking on his thumb. "Take that out of your mouth" his mother demands, but later, while waiting on the platform for their train to arrive, he once again slips his thumb into his mouth. "Would you keep that thumb out of your mouth?", his mother demands. They finally settle into their seats and habit takes over yet again, the little boys mother takes the thumb from her son's mouth and says "Listen, if you keep that up, you'll blow-up like a balloon and pop into a million pieces". This shocks the boy into thinking twice before sticking his thumb into his mouth again.

Just before the train leaves the station, a very pregnant woman struggles down the isle and settles into the seat directly across from the boy and his mother. The lady catches the boy looking wide-eyed at her enormous belly and smiles with motherly pride until the boy looks up with a sly smile and says in a conspiritory tone, "I know what you've been doing!"