i remember it was in the anarchist cook book i think.. I'm not sure, i think it might just pressurize slowly, even if it does, ull get out clean, but when they get in its shaving cream EVERYWHERE.. haha.. im gonna try it...
as when i have done it, the pressure of the car has nothing to do with it
the shaving cream is frozen and wont expand because of this, but as it thaws, it will expand because there isnt a bottom to the can and it just goes everywhere