Final answer:
Adding bacteria like E. coli or food allergens to a burger can upset or harm the consumer due to foodborne illnesses or allergic reactions. Food items must be handled properly, and individuals with food allergies should be cautious about burger ingredients.
Step-by-step explanation:
To address the query of what can be added to a burger that could potentially cause upset, it is essential to consider the implications of food safety and the biology involved in foodborne illnesses. Two substances that, if added or contaminating a burger, could lead to discomfort or illness include bacteria like Escherichia coli or Salmonella, and food allergens such as nuts or shellfish, which could cause allergic reactions in susceptible individuals.
Bacteria can be inadvertently introduced through improper handling or cooking of food items. If ground beef or bagged lettuce for burgers are 'spiked' with bacteria, it could result in food poisoning. Allergens are another factor; ingredients that are safe for most can cause severe reactions in people with allergies. Awareness and caution should be practiced when preparing and adding ingredients to a burger.
For a deeper understanding of this topic, one may refer to the suggested supplementary reading, "Menu of the Future: Insects, Weeds, and Bleeding Veggie Burgers" by McMillan, T. 2018, featured in National Geographic.