converts cats into dogs hehehe
nah, its a 'catalytic converter'. its a 'dholki' with fine platinum coated honeycomb structure inside. Its to catalyze the reaction of harmful CO and NOx gasses and convert them into harmless CO2 and NO2.
It becomes useless/ clogged if eg. leaded petrol is used in the vehicle or if the vehicle burns engine oil or even if the A/F mixture goes wrong and it gets carbonised.