Today, in session, I used one of my guinea pigs peeing on the other as an analogy for something. Dr. T seemed amused by it, but said it was an apt analogy. It was more about how the peed-on pig will expect it to happen, so jumps back, even though it doesn't happen most of the time. (The one doing the peeing aims it like from a water gun--I was stunned the first time I saw it! Both female pigs, incidentally.)