While it's much easier (AKA mainstream) these days to be vegetarian or vegan, there are still a few foods that aren't suitable for these diets that get accidentally slipped into dishes. From candy to sauces to sushi, veggie-centric folks can consume animal products by accident in several ways. Here, a few of these trickiest foods:
Worcestershire Sauce: Sprinkled into everything from Caesar dressing to a Bloody Mary to cocktail sauce, worcestershire sauce is a common ingredient in a lot of restaurants. Anchovies are a main ingredient of the sauce, so those abstaining from fish should avoid anything seasoned with it.
Refried Beans: Traditional refried beans (both in cans and Mexican restaurants) are typically made with animal lard. Always be sure to read the labels (most of the time fat-free types are vegetarian) or ask your server how the beans are cooked.
Omega-Fortified Orange Juices: Something a little fishy is going on with fortified orange juices. Those that contain the added fatty acids usually have fish oil derivatives as the source. Although (thankfully) not detectable in the taste, it does keep vegetarians on their toes and frequently reading the nutrition labels.
Some Candies, Jell-O, and Marshmallows: Once you become vegetarian, it's amazing to realize all the things that meat is quietly snuck into. A lot of those foods contain gelatin, animal bone marrow, and it's used as a thickener in gummy candies, marshmallows, and is the main ingredient in Jell-O. Agar-agar is a good vegetarian replacer and is available in health food stores and Asian grocery stores.
Some Cheeses: Cheese, the (let's all be honest) foundation of most vegetarians' meals, can also contain products that aren't suitable for a meat-free diet. Rennet, an enzyme complex from mammal stomaches, is used to process a lot of cheeses. Many brands of block cheeses are now labeling themselves "vegetarian" to help shoppers find rennet-free products.
Soy Cheese: It's a mistake many beginner vegans make. Assuming that the first package of lactose-free soy cheese they see in the store is vegan-friendly. Most of these brands, made for people with lactose intolerance, contain casein (a milk derivative) to make the slices melt easier. It's easiest to just pick packages that are clearly labeled "vegan."
Pesto: It's green, so it should be automatically vegan-friendly, right? Nope. Most pesto, whether fresh or jarred, has some amount of cheese blended in. It's easiest to make your own at home (just throw fresh herbs, oil, garlic, and some nuts in the food processor) or stick with tomato-based sauces when dining at Italian restaurants.
Non-Fat Yogurt: You thought you were being safe. No fat, no meat, you're all set! But a lot of non-fat yogurts use that lovely reoccurring gelatin as a binding agent. Since there's no fat to make it full bodied, gelatin is turned to as an emulsifier for the yogurt.
Olive Tapenade: Tapas-loving vegetarians, I'm afraid I have some bad news. Olive tapenade traditionally contains anchovies for an extra salty punch. Some jarred varities are vegetarian though, so be sure to read the ingredients list. Or even better yet, visit the olive bar and get a mix of different varities to make your own tapenade.
Vegetable Sushi: Vegetarian sushi is usually very easy to find. Most sushi restaurants have at least avocado or cucumber rolls on the menu, or are willing to make a custom one for you. Just make sure they don't put bonito (dried fish flakes) on top to finish it off, which is common for some establishments.