(i) The French started a massive rat hunt in 1902. (ii) The French offered the Vietnamese cash for catching the rats. Rats were caught in thousands, by May 30 alone 20,000 rats were caught, but the rat menace did not end. (iii) The French paid money when the rat catcher showed a rat tail as proof of a rat killed.The Vietnamese had found an ingenious method of fooling the French. They cut off only the tails of the rats and let them loose with the result their population did not decrease.Some people even began raising rats for money. In the end, the French had to scrap the cash reward. The French had underestimated the intelligence of the local people who joined hands in fighting them. They cared only for the health and hygiene of their own people and it backfired on them.