Apparently, cows in Switzerland have become ornery, and even dangerous, since they have been allowed to spend more time on their own. A surfeit of milk prompted the government to recommend that more cows be raised for meat, and the subsequent reduction in human contact has permitted the cows to conspire against us. Remember, as Troy McClure says: "Don't kid yourself Jimmy. If a cow ever got the chance, he'd eat you and everyone you care about!" On the other hand, maybe they'll just re-evolve into the aurochs, and that would be cool. In the meantime, the article has these recommendations for dealing with an aggressive cow: "They scare easily. If someone stands directly ahead or behind a cow, the risk of being hit is heightened. It is vital that you are seen by the cow, speak softly to it and avoid running or making sudden movements."
Sounds sensible, and more or less the same advice applies to aggressive New Yorkers as well. [Thanks to Gothamist reader Peter G. for the tip]