The smell left by previous trapped rats warn other rats keep away from the mouse trap. KL City Hall should educate the hawkers and traders in wet markets to burn the cage and then immerse in the boiling water after each catch if they want to catch more rats as beginning of the campaign.
It is estimated rat population in the city is same with the human population, therefore at least three million rats living in the KL city. Catching 30,000 rats each year is a fruitless campaign to check and control the rat population.
I think at least 300,000 rats should be wiped out each year from KL city.