One evening, little Johnny was with his mother in the bath. He pointed at 
his mother's breasts,and asked what it was. She told him that they were 
balloons,and when someone will try to blow them up, they'd go in the air, 
straight to heaven. 

About two days later,Johnny ran into the kitchen and screams, "Mother, mother, 
come and look! Sister is dying!!!" 

Why,asked his mother."Because her boyfriend is on top of her, blowing her 
balloons, and she's screaming-Oh God, I'm coming."