Cow farts may be a way for astronomical ETI on other worlds to know that there is life on Earth, as methane is usually only produced in large amounts by organisms. There are other ways to tell remotely if a planet has life or not, but the cows' role in this is always enlightening, to say nothing of amusing.

So that's why it's always cows getting mutilated....

Cue X-Files theme music.

To keep this on topic, maybe smokers, by sacrificing their lives, will also put enough artificial chemicals into Earth's atmosphere to make an ETI civilization know that someone is on this planet and cause them to contact us, thus bringing us into the higher Galactic Realm.