I heard it like this....
A young boy was to be in a play, his line was," Hark, I thought I heard a pistol shot, there she sits, a young lass with her soul full of hope, I think I will snatch a kiss and run off into the woods." But on the day of the play, seeing all the peolpe in the audience and getting very nervous he stammers," Hark, I thought I heard a possum fart, there she sits on her ass with her hole full of soap, I think I will kiss her snatch and shoot off into the woods.....