<P> A widget is a device placed in a container of beer to manage the characteristics of the beer 's head . The original widget was patented in Ireland by Guinness . The `` floating widget '' is found in cans of beer as a hollow plastic sphere , approximately 3 cm in diameter ( similar in appearance to table tennis ball , but smaller ) with at least one small hole and a seam . The `` rocket widget '' is found in bottles , 7 cm in length with the small hole at the bottom . </P>
why is there a ball in guinness beer
to manage the characteristics of the beer 's head