Trouble at the Yard Sale — William Kotzwinkle

Walter's family is holding a yard sale, but there are few customers.  Walter, farting contentedly near Father, wonders why.  When a man offers ten dollars for Walter, Father readily agrees.  Walter wonders why.  Walter is sad to leave his family behind, but relieved to discover that his new owner is a clown.  Walter figures he will help the clown bring joy to children on their birthdays.  But the clown has a dastardly plot: he will use Walter's gas to inflate balloons and then pop them to stun guards during bank robberies.  Will Walter turn to the dark side?  Of course not! He comes out a hero is reunited with his family by doing what he does best.