I was commenting on a blogger post just now, and I filled in the captcha and then pressed tab onto the first radio button and enter to submit the form. Except instead of submitting, suddenly my computer said "beep, beep, beep" and sounded a cacophony of voices. I was completely bewildered at having caught a virus that tuned my computer into a schizophrenic numbers station until I realized that I'd activated the audio captcha.