A while ago I had posted on verification process using few scientific questions to separate humans and spambots.
Now Brain Hayes has few questions to distinguish spambots. The good thing is you learn some new things even if you are unable to comment 🙂 .
Sample these few questions form his blog. (Currently the questions seems to be very few in number, I wish to see lot of variety in it shortly). As for my blog is concerned, spammers are caught by Akismet. It is too good, it has blocked all the spams and there is no false positive yet!
- Which is larger, 0 or 1?
- 1 + 1/2 + 1/4 + 1/8 +….?
- 0 1 1 2 3 5 8 …?
- Square root of 169
- Who published the first prrof of the impossibility of trisecting an angle?
SKB 
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It may not be intuitive, ambiguous at time, but what could you expect from him 🙂
BAD DESIGN….. it is non intutive.
it would be very hard to explain it to a common man who does not like maths….