"One day, a student noticed something strange: One of the rats in the group trained to expect positive experiences had its tail straight up with a crook at the end, resembling the handle of an old-fashioned umbrella."<p>For anyone having, being friends with, are interested in cats will recognize this behavior. If you meet a cat on the street and it raises its tail like this, it will also probably come up to you. A cat that sweeps the tail back and fort, often with the end of it a bit jerky is probably afraid, angry, hesitant and does not want to engage. It should be left alone unless you want to feel the sharp end of those retractable razor blades.<p>Cats also use the same patterns between each other. And interestingly some dogs use the same patterns too. Tiger puppies seem to do this also (as seen in documentaries). So, at least to me, there seems to be common 'language' to express feelings and interests between some animals equipped with tails.<p>I would have thought this should have been a known thing, possibly even for the driving rat scientists. Anybody on HN that have some references into known ´tail language´?