• There is at least one other rearrangement of a dartboard in which each neighbouring pair adds up to a square number: 20, 18, 15, 10, 6, 19, 17, 8, 1, 3, 13, 12, 4, 5, 11, 14, 2, 7, 9, 16 (Puzzle, 28 September; solution, 5 October).
• Tardigrades, or “water bears”, have eight legs (12 October, p 34).
