There is Gold in them thar Cow Plops!!!
At least that is what this National Film Board short seems to suggest, where an inventor has come up with a good way to extract methane from cow plops, which is usable with cars and such.
The description of the short does it justice:
This short film presents Mr. Bate, an inventor who discovers a substitute for gasoline in barnyard manure. Even though he fits the classic mould of single-minded know-how and practical dreamer, his discovery is tried and tested. He demonstrates how his homemade digester does turn manure into potent methane gas that powers his auto. And for good measure, he demonstrates his latest sustainable invention â€“ a bicycle powered by the bumps on the road.
Now that is what I call a GREEN solution to a problem. Given we need cows anyhow, why not use their DUNG for fun?