lucy24 - 11:53 pm on Feb 1, 2012 (gmt 0)
Question: If I ask you if this path is safe, what will you answer?
Path A / Guard A's answer: Yes. (truthful)
Path B / Guard B's answer: Yes. (liar)
How could you know from that?
Your question is not "Is this path safe?" It is "What would you say if I asked?" Guard B therefore lies twice: "I would say yes" = He would really say No = The path is safe. And vice versa.
You know you're addicted to the Internet when you have a decimal-to-hexadecimal converter bookmarked, telling you that 8226 = x2022 = bullet.