its because smoke is a bunch of tiny molecules that are about the same mass as air, they float around and when you let them float around too long they start sticking together to form larger molecules and so when you inhale after the smoke has had a chance to "coagulate" the smoke is much thicker and denser and makes u cough more.

thats why
God v2.0 Reviewed by God v2.0 on . Stale smoke...? ok, so u know wen u take a hit from the bong, and sometimes theres that "devil smoke" or "ghost" left in the bong, which is basicaly stale smoke that if u inhale, it tastes so bad, and makes u cough? can some1 explain the science behind this? Rating: 5