Eating corned beef isn’t the only activity off the menu for vegans and vegetarians on Saint Patrick’s Day. Drinking Guinness, which is essentially the holiday’s main event, is also out of bounds. Isinglass, a substance made from dried fish bladders, is a type of collagen used by some breweries, including Guiness, to filter beer. The Irish brand has used this method since the mid- to late-19th century, so if you’ve had a Guinness in your lifetime, you were sipping on faint traces of bladder. If you are upset to have learned this fact, just have a few Guinness, and after a few sad toasts, you’ll soon forget those poor bladderless fish.