Okay, hopefully you watched the movie at least once before looking for this slip-up. When the "flubberized" bowling ball and golf ball first shoot up into the sky, they come back down onto the pavement in front of the garage. This stays accurate throughout the movie-UNTIL the end! When the professor is getting married via video camera, and blows the house up, the balls bounce in the walkway to his front door! Must've hit a plane and changed course, I guess...