1) British game show 2) Difficult puzzle 3) Knot 4) Mental challenge 5) Puzzle 6) Riddle 1) Enigma 2) Mystery 3) Poser 4) Problem 5) Puzzle 
BrainTeaser was a British game show, first broadcast in 2002, produced by Endemol UK subsidiary Cheetah Productions. BrainTeaser was live, with phone-in viewer puzzles being announced and played during the show in addition to the studio game. During its run until 7 March 2007, it aired on Channel 5 Mondays to Fridays, usually for an hour around lu... The word brainteaser means a playful puzzle posed as a test of intelligence. ...
a puzzle or problem whose solution requires great ingenuity.