You're right! It was a trick question. Snoopy never has talked. Readers can see what he's thinking via thought balloons, but he isn't actually shown to be speaking. During the strip's first few years, Snoopy was an excitable but fairly conventional beagle without a thought or word in his head. Later the thought balloons ushered in a whole new dimension for Schulz and his characters--now Snoopy could be seen fantasizing about flying Sopwith Camels in battles with the Red Baron during World War I, etc.
