Courtesy of Curiosity.com:
“Are you logical? Maybe that’s a trick question, because we’re talking about deceptively difficult logic puzzles. This problem presented by Presh Talwalkar of the MindYourDecisions YouTube channel will test your thinking skills.
The following words are written on a chalkboard: cat, dog, has, max, dim, tag. Albert, Bernard, and Cheryl each have a strip of paper. Each strip has a different letter from the secret word, which is one of the words on the board. First, Albert says, “I know the secret word.” Then Bernard says, “Now I know the secret word.” Finally, Cheryl says, “Now I know the secret word.” All three people are perfect logicians. Which one is the secret word?”