Yup, Clay's right....take some gravel and unpopped popcorn in your hand. Squeeze and roll it around awhile (if you like you can toss in an optional grasshopper, couple of grubs, a potato peel--cooked if you like--, a wormy tomato...). Squish it around for an hour or so. Then see how much of the corn remains uncracked.
That's a gizzard.
...that was an icky visual...excuse me while I wash my hands vigerously!
That's a gizzard.

...that was an icky visual...excuse me while I wash my hands vigerously!