How would you distinguish the man from the machine?
Humans use rapport to sniff out artifice
Essentially this means that it will always take a series of questions and subsequent analysis of the answers to establish if the anonymous entity at the end of the line is a human being or not. A single question will not achieve this.
I suppose you could ask "Will you meet me in the car park in 2 minutes?" and then see what turns up.
You’re in a desert walking along in the sand when all of the sudden you look down, and you see a tortoise, it’s crawling toward you. You reach down, you flip the tortoise over on its back. The tortoise lays on its back, its belly baking in the hot sun, beating its legs trying to turn itself over, but it can’t, not without your help. But you’re not helping. Why is that?
"Why are manhole covers round?"
Perhaps followed up with "Where do you see yourself in 5 years?"
EDIT: I've come to think of that Douglas Hofstadter has done a delightful piece on this exact subject (including the highest rated answer) and found an online version at http://www.cse.unr.edu/~sushil/class/ai/papers/coffeehouse.html. Especially the scenario where he tries to disclose Nicolai in the "Post Scriptum" section is a fantastic read. I believe I read this in Metamagical Themes.
"Will your answer to this question be negative?"
Note: the original Turing test proposal was for the computer to pretend to be a woman, the interviewer to be a man, and the test limited to five minutes. If the man was unable to determine if the computer was a woman or not in five minutes, we would have to conclude that the computer was intelligent, "because the converse is not polite".
Well most likely computer has problem answering an alternative to problem :
"When was the last time you prevaricated?"
Semantically it's a sensible question, and a computer would probably try and answer it, but a human being would just say - "Awee... c'mon.. how the hell would I know?"
Anything with that pattern, ie. linguistically, semantically, and culturally a sensible question, but something which no real person would ask, or answer. (This can be done, without going into deeply personal areas - in fact, the computer might be programmed to handle those with "that's private").
I would ask anything where there isn't a clear cut answer and which usually involves strong or varied opinions and/or emotions from human participants. For example:
- What do do you think of the current situation in Libya?
- What are your thoughts on the recent disaster in Japan?
- How do you think we should resolve the humanitarian crisis in the Ivory Coast?
- Why do you think Coldplay became so popular?
- What do you think about Charlie Sheen?
- What new technologies should we foresee in the next twenty years?