
The Great Rat Tail Trick
Would you rather be paid for catching rats, or for growing them?
Hanoi, 1902. The French ruled the city, in today's Vietnam, and had built shiny new sewers. Rats loved them. They popped up through flush toilets into fancy villas, and rat fleas could spread plague.
For you, before dinner
This is the cleanest real example of a perverse incentive: a reward that makes people do the opposite of what it was designed for. Once kids see it, they spot it everywhere, from star charts to school points.
Try it tonight
Everyone names one reward at home or school: stars, points, stickers, pocket money. Go round the table and, for each one, find a sneaky way to 'win' it without doing what it was meant for. Fastest loophole wins.
Three questions for the table
- About you
Have you ever earned a reward without really doing the thing it was meant for?
- Think it through
The cobra story may be a legend. How would you check whether it really happened?
- Pick a side
Design a rat bounty nobody can cheat. Then swap plans and try to break each other's.






