THE GAG TEST
Anything that makes you gag is spoiled (except for leftovers from what you cooked for yourself last night).
When something starts pecking its way out of the shell, the egg is probably past its prime.
If opening the refrigerator door causes stray animals from a three-block radius to congregate outside your house, the meat is spoiled.
Any canned goods that have become the size or shape of a basketball should be disposed of. Carefully.
It should not taste like salad dressing.
Fresh potatoes do not have roots, branches, or dense, leafy undergrowth.
GENERAL RULE OF THUMB: Most food cannot be kept longer than the average life span of a hamster. Keep a hamster in your refrigerator to gauge this.