Its so simlpe its not funny....

because after you have smoked it your head feels like its been cooked in one..

Because in the 1920's they used to ship it from Afganistan and neighbouring countrys in clay Pots...

Its an old school code word thats better known these days and is no longer a code word..
Like titties in Jail..

weres the Myth busters when you need em.?.
you decide.

A.
B.
C.