Yeah, it's rather easy too.
I mean -- the entire CAPTCHA system wasn't made to be a pain. It's actually a way of transcribing books and illegible documents. You see, we have masses of print archives. We run these archives through computers which scan and transcribe everything digitally. However, there are many words that are skewed & illegible to a computer's scanner. It takes a human to decode it.
This is what CAPTCHA is. CAPTCHA provides one word (that it knows the answer to) which you must get correct. The second word is something that needs to be read by human eyes -- that way they can piece it in with the rest of the document. It's practically free labor. Websites keep the site bot free -- archives get loaded up with information and decoded.
Try it yourself. Next time you're in CAPTCHA -- try finding the word that is easy to read. This is the "puzzle" word. The word that you must get correct -- otherwise, the entire thing is wrong. Now find the second harder to read word. This is the transcribe word. You can literally type anything you want here (reasonably) and it'll still accept your CAPTCHA answer.
And that kids is how it works.