It depends on how you define herbivore. If being herbivore meant having your diet made up of 100% of plant matter then I could define cows, giraffes, deer, dugongs as omnivores and not herbivores. Imagine how many insects a cow can ingest in its lifetime while munching on grass. Imagine how many snails a dugong would ingest while grazing on seaweed. While emerald crabs are stated as herbivores...I am certain they will feed on animal protein if given the chance when they are hungry.