Barbs are wrapped around the twin wires, yes, but the twin wires are already touching each other. But a fence will usually have more than one strand of wire (though not always barbed) - I imagine one stand was Tx and a different strand was Rx.

Yes. That was more or less how he did it.

Spliced some coax to alligator clips. One strand for the inner, one strand for the outer (if memory serves).

Cisco actually demonstrated Ethernet over barbed wire (and other materials) back in '02.

http://slashdot.org/story/02/01/03/2039218/ethernet-over-ass...