Can you find some concrete indications and check for them in a blind test?
That would go a long way towards a general 'proof' that something exists which can be described as internal skill.
I think this is a great idea. And we could easily do it. It however might be rude at a seminar to suggest we do a blind test, and probably out of the scope for what I'm asking. But on a side note, I would love to do it if any IP experts were up to it.