"Man is the only creature that consumes without producing." How does Old Major prove this in Animal Farm?
Old Major is pointing to the fact that the animals do all of the work on the farm but reap none of its benefits. This was also a key idea of Karl Marx, who wrote helped write Communist Manifesto. Marx's point was that workers should be able to share in the fruits of their labor. Old Major is making a similar point that the animals should be able to share in the profits from the farm. Instead, Jones takes all the profits and makes the animals (his workers), do all the work and doesn't even feed them properly.
To prove this assertion, we need to look at the text of Old Major's speech in Chapter One. After making this comment, for example, he goes on to say that:
He does not give milk, he does not lay eggs, he is too weak to pull the plough, he cannot run fast enough to catch rabbits.
In other words, Old Major refers to the biological differences between Man and other animal species. He reinforces this in the next paragraph when he argues that Man is "lord of all the animals." In other words, Man's only achievement is his ability to turn animals into his own personal workforce: he organises them, puts them to work and then profits from the items they produce.
In asserting this point about Man, Old Major incites rebellion against Mr Jones because he successfully argues that they are the victims of human exploitation and, by overthrowing him, they can take back the fruits of their labour.