Butyl rubber, commonly used in gum (as well as tires and basketballs, mm!), is a synthetic rubber that provides it with an ideal chewiness. You’ve probably noticed that gum is unaffected by the crushing of your teeth - that’s kind of the point. So when you swallow the gum, it moves through your digestive tract into your stomach as one giant wad. While your enzymes are able to break down the carbohydrates, oils, and alcohols in the gum as they would with regular food, the rubber base in the gum is basically immune to these enzymes.