Gutter oil is a general term for all kinds of inferior oils. In a narrow sense, gutter oil refers to the oily floating objects in sewers or the leftovers of hotels and restaurants (commonly known as swill) which are simply processed and refined; Salad oil, commonly known as salad oil, is a refined edible oil refined from crude oil. Eating gutter oil can lead to indigestion, diarrhea, severe abdominal pain, gastric cancer, intestinal cancer and so on.