[rbanffy]

We can always make the understanding of metaphors a required step for signing up.

[opminion]

Tongue-in-cheek, how hard would be to make a captcha?

Examples from [1]:

Metaphor: Argument is war I shot down his argument He couldn't defend his position She attacked my theory

Love is a journey: Our marriage is at a crossroads We've come a long way together He decided to bail out of the relationship

[1] http://pinker.wjh.harvard.edu/articles/media/2006_09_30_then...