Mad cow disease highlights an interesting dimension of networks (or processes, which can be viewed through the lens of network science). This was prompted after reading an interview with John Stauber and Sheldon Rampton, authors of Mad Cow, USA: Could the Nightmare Happen Here?, from 1998(!).

Economies, or sectors of the economies, can be seen as networks of buyers and sellers. The production process is a circuit of connections between suppliers, producers and consumers. Food chains are ecological networks. In the agricultural sector, these bundles of connections all overlap.

Per the interview above, mad cow disease (MCD) became a problem when the life of the cow became a closed circuit -- farmers, to boost protein in the diet of cows (because the bovine growth hormone being injected into the cows worked best w/ a high protein diet -- chains of causality) fed chopped up, rendered cow parts to the herd, turning them into unwitting cannibals. Dead cows were fed to living cows, so the relatively rare spongy brain problem was fed back into the system, increasing the likelihood of the problem intensifying. Per Sheldon Rampton: "And that could create a closed amplification loop". AKA a positive feedback loop, like you get when you hold a microphone too close to the speaker it is connected to.

The nature of interactions in a network then can be of a positive feedback nature (not always a bad thing) or of a negative feedback nature (like the thermostat in the home -- if the temperature gets to hot, it triggers an event that causes the temperature to drop). Leaps are associated with positive feedback loops; normal development with negative feedback loops.

MCD is a confluence of technological revolution (the genetically-engineered growth hormone) and capitalism (maximization of profit demands new technology whether safe or not for humans and other living things, and requires the re-organization of production around the new technology to squeeze of the maximum profit).

Another interesting dimension of MCD is the disease itself -- MCD is caused not by a bacteria or virus, but rather by a mutant protein. It's not a living thing as such, and standard sterilization practices (including heat, irradiation and or most chemicals) cannot eradicate it, which enables the disease to survive the rigors of the rendering process by which dead cows are turned into food for live cows. Called "prions" (see "Prion Diseases" for more info), these mutant proteins somehow interact with normal proteins causing the normal ones to turn into prions. (Another kind of interaction, in this case in the network of protein interactions within the brain). The result is the disintegration of the brain; holes developing in the middle of it, hence "spongiform".