I find I am not the only one to crave chocolate during my monthlies.

It seems to contain a unique composition of caffeine, serotonin, probably some minerals and simply sugar, that really makes you feel better.

Is there any evidence of a food/sweet that could pretend on that role before chocolate was invented?

Foil wrapped chocolate rabbits comprise a highly inflammable aluminium wrapper, surrounding chocolate which melts at slightly above ambient temperatures.  Together the chocolate and the foil completely enclose an air space. 

When heated up, one could imagine either that the enclosed air would expand, leading to an explosion, or the aluminium might catch fire, or the chocolate would melt before either of the other catastrophies. Is it known under what circumstances each process dominates?

Sometimes it also appears to exhibit pitting (with no visible insects to be found -- though it's unclear, with all the packaging, if some of the pits were developed during manufacturing) and a slightly rancid (?) taste. White chocolate of similar age seems to be less affected. Caramel centers in chocolate seem to dry out with time, leaving a dry residue.

Chocolate can melt in one's hand, but slight cooling can also make it hard enough to damage some dental work. What accounts for such change?