I saw a comment form recently where there was a field labeled 'Are you human?', if you enter 'yes' your comment is not marked as spam. I wonder how well silly b

I saw a comment form recently where there was a field labeled 'Are you human?', if you enter 'yes' your comment is not marked as spam. I wonder how well silly but obvious questions, to humans at least, can stop spam? From a UX perspective it's slightly less effort than deciphering a CAPTCHA box. It's not as thorough a solution as CAPTCHA but is super quick to implement.