Killer Instinct

Killer Sudoku is one of the very few things to have been designated 'killer'.

Killer bees, otherwise know as Africanised honey bees, get their reputation because of their extremely defensive behaviour. They are more likely than their European cousins to attack and pursue a perceived threat (person or animal) for up to a mile, stinging it remorselessly all the while. Whether this behaviour is sufficient grounds for a 'killer' reputation is debatable (their sting is no more potent than that of other bees) but the name does serve as a useful warning to ramblers.

Killer whales hunt in groups (or pods) and adopt a range of cunning techniques to catch prey. For example, they baffle fish with a fizz of bubbles, they work in relay to chase young whales to exhaustion, and they also join forces to tip unsuspecting seals off icebergs. They are the largest members of the dolphin family, but this does not stop them from snacking on other dolphins; and they will also munch on whales, sea lions, even birds. Killer whales are not a great threat to humans, but they do live up to their reputation.

Killer Sudoku is a formidable challenge, not to be taken lightly. It will not cause you much physical damage, but it will certainly chew up your thoughts. Please don't take this personally: the puzzle is just acting in accordance with its instincts.