How Many Liars?

Molly Ride, pilot of the spacecraft, knew that some Martians were truth-tellers and some were not. So when she came face to face with three of them, she asked, 'Are you truth-tellers?" The finned Martian answered her by rubbing his stomach. His friend, a tall Martian with feathered ears, told her that the finned Martian had said he was a truth-teller. However, the other Martian, who had horns, said that the finned Martian was lying. How many of these Martians were liars?

Answer:

One. Since the finned Martian did indicate that he was a truth-teller, then the Martian with feathered ears was obviously telling the truth and must be a truth-teller. If the finned Martian was lying, then the horned Martian was a truth-teller. If the finned Martian was a truth-teller, then the horned Martian was a liar. So, no matter how you look at it, two of the three Martians were truth-tellers and one was a liar.