Okay, they compare them by how much land/energy it takes to produce the food/fuel. I would be interested how they came upon their figures for fossil fuels. But my main concern is that they never mention emissions. The main concern with cars isn't so much how much fuel they use, but how much pollution they put out...
Also, it seems they didn't factor in producing the vehicles, which also uses a lot of energy and puts out a lot of pollution. Factor those in and I'm sure pets will turn out much cleaner by orders of magnitude...
Oh, and did I mention pets are "biodegradable", unlike cars ?
If the aborigine drafted an IQ test, all of Western civilization would presumably flunk it. -- Stanley Garn