There are plenty of terrible ways to get sick and/or die, and foodborne botulism is pretty high up on the list. One minute, you're spooning lovingly home-canned sauce onto your plate—or in the tragic cases of 10 people near Sacramento, California, pouring gas station nacho cheese onto your chips—and within 12 to 72 hours, your life is forever altered or even possibly ended. When food (especially low-acid mixtures) is improperly processed or stored, Clostridium botulinum bacteria can grow quite rapidly and release a nerve toxin that wreaks havoc upon the human body. Botulism poisoning can manifest as vomiting, blurred vision, drooping eyelids, slurred speech, difficulty breathing, and muscle weakness. It can cause gradual paralysis or even death, and often there's generally no way for a consumer to definitively tell if a food has been infected with botulism or not.
Foodborne botulism is rare, though. This info is not meant to scare you away from accepting generous gifts of your Aunt Zelda's homemade tomato sauce or, horror of horrors, lead a nacho-free existence. But it helps to know a few food safety basics in order to minimize the likelihood of ingesting infected food or inadvertently inflicting this brand of sickness upon your loved ones.
Per the US Department of Health and Human Services, the most common conduits of botulism are: home-canned foods with a low acid content (like green beans, asparagus, beets, and corn), improperly canned commercial foods, home-canned or fermented fish, herb-infused oils, baked potatoes in aluminum foil, cheese sauce, bottled garlic, and foods held warm for extended periods of time. To avoid contamination from commercial foods, the USDA recommends examining packages at the store to make sure that they don't appear to have thawed and re-frozen, and that they haven't punctured, torn, or been otherwise damaged to expose the contents. If it's gassy or spoiled, they also advise not to buy, but seriously, you knew that.
Once you get the food home, don't use it if it's discolored, moldy, or has an "off" odor. Additionally, the USDA advises, "Do not use products that spurt liquid or foam when the container is opened." and above all, don't taste it to see if it's OK. Your life is worth more than some discount chili.
The Centers for Disease Control and Prevention also notes that it's important to keep oils infused with garlic or herbs in the refrigerator, and keep baked potatoes wrapped in foil hot until serving, If you suspect that the food has been contaminated, throw it out immediately, scrub everything it may have come into contact with (including surfaces and utensils) using a bleach solution, throw away any sponges or cloths you used to clean it up, and immediately launder anything you were wearing that it may have splattered on.
As for the homemade stuff, it's crucial to follow approved canning guidelines—we've got a primer right here—and observe the same sensory guidelines you would with commercial products. And if it's a low-acid food or anything containing tomatoes, boil it for 10 minutes before serving, even if it doesn't seem suspect.
Side note: The risk of botulism is why you should never feed honey to a baby younger than 12 months old. The bacterial spores that cause infant botulism are often present in honey, and they can activate and produce botulinum toxin inside a baby's large intestine. It's fine, however, for a breastfeeding mother to eat honey because the spores are too large to be passed through milk.