Wait a minute! Who would want to rehydrate popcorn? It's dry for a reason, right?
Wrong! Popcorn pops into light, fluffy kernels because it ISN'T dry...all the way.
The moisture in the kernels is what heats up, and bursts the kernels.
So if you have some popcorn that's been stored for awhile under less than ideal conditions, it's going to have dried out to the point where you get half-popped kernels, or lots of "old maids".
So here's the solution:
Fill a 1 quart Mason jar 2/3 full of old popcorn.
Add 2 Tablespoons of water
Seal the lid and shake the jar until you can't see any sign of moisture inside
Let it sit sealed for 2-3 days, and pop as usual