The USDA requires pet food manufacturers to list ingredients in order of predominance the way the product is to be used in the pet food.
Many manufacturers try to disguise an ingredients volume by using different forms of the same ingredient. Using corn as an example, look on your food label for different variations. Such as:
ground yellow corn; chicken by products; corn meal; chicken by-product meal; corn gluten…
If you added those three types of corn together you could end up with a higher net weight of corn than any other ingredient.
Start reading your pet labels more closely!