Bio experiments
There's an open question as to where viruses originally came from. Did they coevolve with bacteria, or are modern viruses things which spontaneously came into existence in the recent past?

Here's an interesting experiment which might shed some light on the issue: Create an environment which is very amenable to bacterial growth, meaning plenting of oxygen, water, heat, and nutrients, but in which there are no life forms whatsoever. Then introduce a single bacterium, and let it grow for many generations. At the end, check to see if any viruses have appeared.

And here's an unrelated experiment in psychology. Let us say that we wish to measure just how bad a bias an experiment not being double-blind would create. For the purposes of this experiment, we ask for volunteers to be both testers and testees in a sham experiment having to do with subliminal messaging. The subject is shown a flash of something, and the tester is shown what it was but the testee is not. Of course, there isn't ever any actual subliminal message shown - the experiment is to see how much the testee guesses correlate with what the tester thinks the testee saw.

Such meta-testing is done quite rarely. Whether males and females interpret the meanings of numbers in a 1 to 5 scale is, so far as I know, a completely untested area, making a very large field of survey-based gender psychology extremely dubious. The book Monkeyluv, which I highly recommend, has a section talking about a meta-study of controlled rat experiments where multiple groups attempted to raised rats under exactly identical conditions and then measure various standard traits about them, and the results indicate that many important traits, including some which various drugs are prescribed to control, are mostly controlled environmentally. The study's implications have unfortunately been mostly ignored.