The video is to prove a point really fast, but, cows actually do only eat proteins. They have three stomachs that they use to feed grass to bacterial colonies, which they then pull into their fourth stomach to eat, with any of the grass that's left un-eaten by the bacteria being shit straight out without being processed any further. They don't eat the grass, the grass is there to feed what they do eat, which is supplemented by eating any large animal small enough to fit in their mouth. I read a study once that almost all cows when dissected had at least 1 animal in their digestive system at a time.

The notion that cows are good peaceful harmless herbivores who eat nothing but grass is nonsense. Here's a video of a cow eating the corpse of a donkey. Of note: there's grass right next to the body. And it isn't just a result of cows being fucked up by human domestication, wild deer (who you cannot blame on humans malnourishing it or contaminating its feed or whatever) do it too.

constructing an elaborate worldview out of a kindergarten level understanding of biology and then getting extremely smug about it annoys me relentlessly. Cows would eat you if they had the chance