The "Are you human" verification is required when performing certain actions on a Stack Exchange site we're not logged in to, such as performing a search.
Are you a human being?
We apologize for the confusion, but we can't quite tell if you're a person or a script.
To be fair, it's pretty quick and painless, just needing to click in a tick box, and it seems to last for the duration of that visit.
However, it would be much better if the scripts which request the verification could instead check if we are logged in to another Stack Exchange Network site.
Since the new login system already recognizes logged-in users and invites them to "join this community" (photo credit Normal Human), it's an obvious lie to claim "we can't tell if you're human".
Although status-declined, seems some recent changes in the code have inadvertently resolved this issue. I've not seen a request for captcha when visiting a site I'm not registered with and am logged in to another site.
Seems like the Unicorns defeat evil once again...