I am just a casual observer, but how did they narrow it down to the way the rats were touched? Couldn't it have just been the people "running" the experiments instead being more casual about their results? Maybe for a dumb rat you hit your stopwatch a second later or a second faster for a smart rat, for example.
How did they isolate the touch of the experimenters?
I can't speak for that study in particular, but it doesn't really matter if it was the touch so long as it was not a measurement effect. There has been a decent amount of research on the Pygmalion effect in varying contexts; it's opposite, the Golem effect, has had its share of research too. It's not an obscure phenomenon at this point.
Yes I too was interested to know how they eliminated bias. If you were told one rat was smarter than the other, surely there's a risk of influencing the interpretation of results.
How did they isolate the touch of the experimenters?