Around 1998 I was working for a small mom and pop computer/networking shop and had a customer successfully run Ethernet over barbed wire so he could network between his house (where the main computer was) and his barn.
It was about a fifty foot run at 1Mbps. He did have issues when it rained, once the posts got wet enough to ground the wires.
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.
It was about a fifty foot run at 1Mbps. He did have issues when it rained, once the posts got wet enough to ground the wires.