Here is what you do:
Ask a grown-up the following questions. Tell them its part of an important nationwide survey and thank them for participating.
1. Think of some country that starts with D. Don't tell me what it is. (A typical grown-up will think it is Denmark).
2. Take the last letter of that country and think of any animal that starts with it. Again, don't tell me what it is. (A typical grown-up will think kangaroo).
3. Take the last letter of that animal and think of a fruit that starts with it. Don't say anything, just think. (A typical grown-up will think orange).
Finally put your hand on their forehead, close your eyes, and say the following: "Orange...you're thinking of an orange."
Try it out and let me know if it works on others!