"Do you always believe what you see?" asked Snorkel, taking four cards from a regular pack of playing cards and discarding the rest. "What do you mean?" replied Twanger. Snorkel showed Twanger his four cards : an ace, a three, a ten and a jack. After secretly arranging them in a certain order, he dealt them face down in a line on the table. "I've seen this trick before!" cried Twanger. "You want me to tell you where the jack is." "The jack!" exclaimed Snorkel. "There are two jacks in these four cards." How is it possible and where are they in the four face-down cards?