I still think the worst thing about the audio CAPTCHA and a sign that they really didn't test it as well as they shulod have is that they did almost too good of a job in making the noise sound like the signal. Or, in other words, the background noise sometimes ends up sounding like exactly what you're supposed to be listening for.I have auditory processing issues that affect hearing speech above background noise, but when I know i'm supposed to be listening specifically for digits, that drastically lowers the search space. However, I've tried the audio CAPTCHA a couple times when I couldn't decipher the visual one, and sometimes it's hard to tell whether or not the digit I heard was actually part of the foreground. It's very easy to accidentally generate a two in background noise; that's just two phonemes to combine! And since the background noise seems to be English speech played backwards, it's fairly easy to accidentally generate one ( no played backwards!) and possibly eight as well.I guess none of their natural language processing researchers were on hand when they developed this CAPTCHA ^_^