This is better than most brain teaser pages. My pet peeve is the riddles that say “I can’t see which is the right answer,” to which somebody else says he now knows the right answer. Possibly true if the first person thinks deeply about the answer and determines that the evidence is ambiguous, but then again, maybe he doesn’t see the right answer, and can’t even if it’s staring him in the face.
As for the knave and the knight, if the knave picks the door with the lion, you’re now facing a slightly less hungry lion armed only with a sword. If you give the sword back to the knight, will he protect you, or just go get the treasure himself while you’re being the second course?