Listen closely when you pop open a can of Guinness Draught Stout, and you’ll hear a peculiar rattling sound. No, your can is not defective. In fact, that tiny ball — or widget — is doing the work to give your brew its signature creamy head, akin to the two-part pour you’ll get at a pub.

Contrary to speculation, these widgets are not filled with nitrogen. At the time of manufacturing, an empty widget is placed inside each can. As the cans are filled with beer and sealed, so are the widgets. As soon as the can is opened, a combination of chemical reactions and ingenious product design forces the beer that’s inside the widget out of it, producing highly nitrogenated beer.

Soon after debuting the widget, Guinness snagged the Queen’s Award for Technological Achievement in 1991.

Get the latest in beer, wine, and cocktail culture sent straight to your inbox.

Ryan Wagner, interim marketing manager at Guinness Open Gate Brewery told Hop Culture that the process is time sensitive, meaning you should pour immediately or risk losing that creamy white head.

“Once you lose that initial rush from the can being opened, you can’t recreate it,” he said.