When the fertilized egg burrows into the uterine lining ?

Between four to six days after conception, the fertilized egg will develop into a blastocyst and burrow into the uterine lining, attaching itself firmly. In this early stage, the embryo develops a yolk sac, which provides its first nutrients.
I found on safari

Smoking damages the respiratory system by inhalation of a foreign substance, that is absorbed and residue is left behind on our lungs sponge like substance. the gas that is inhaled also increase your blood pressure and dilates your blood vessels. also the process of inhaling and exhaling the smoke it causes irritation to the throat and mouth. smoking can cause lung cancer and other respiratory and circulatory diseases.