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There are plenty of things you should lick in this world: Ice cream from the ice cream truck, the salt on a frosty margarita, a candy cane around the holidays, if you like peppermint.
But there are a number of things you really should not put your tongue on. Item: In Japan, people are licking each others eyeballs, a new fad called oculolinctus. The result? A spike in eye infections, scratches, styes and general eyepatch wearing.
With this in mind, we offer a list of 5 other things you shouldn't lick, plus a couple you really should.
The skin of the Colorado River toad (aka Sonoran Desert toad) carries a powerful toxin.Getty Images
Some toads produce a powerful hallucinogen called bufotoxin, which can produce a serious high. A number of human deaths have been reported among those who used frogs recreationally, due to an overdose of the venom.
In California, possession of Colorado River Toads is illegal due to illicit toad licking. Consider yourself notified.
Whoever came up with "5-second rule" had probably just dropped an entire cookie on the ground and needed a sanitary excuse to save it.
When MythBusters Jamie Hyneman and Adam Savage analyzed food-free contact plates that had spent 2- and 6-second intervals on a contaminated surface, the "5-second rule" quickly crumbled. Even if something spends a mere millisecond on the floor, it attracts bacteria. How dirty it gets depends on the food's moisture, surface geometry and floor condition -- not time.
We're going to go ahead and loop in other things that have been on the floor -- like shoes -- and take them off the table, in terms of licking.
The spoon used to mix custard, cake batter, egg nog -- really, anything with a raw egg base -- should not be licked. The eggs need to be heated to 160 degrees Fahrenheit to avoid toxic salmonella bacteria.
This is especially true for anything served to young children, the elderly and people with weakened immune systems.
In 2011, the CDC reported an outbreak of a nasty type of E. coli that made 77 people sick in 30 states. And the culprit wasn't eggs or dairy -- it was raw flour in ready-to-bake cookie dough.
The FDA recommends cooking the dough before tasting to kill harmful bacteria. And you should also wash your hands after touching raw dough.
You can lick a big honking D battery until your tongue is dry. Not much will happen. But if you lick a rectangular 9-volt battery, touching both the positive and negative terminals, you will receive a small electric shock.
Truth be told, it's not really bad for you, just mildly alarming and unpleasant.
By testing bacterial growth in petri dishes using sterilized chips and a salsa-like substance, MythBusters Savage and Hyneman found that double-dipping adds just a small amount of bacteria to the salsa, and definitely not as much as sticking your mouth in the bowl.
The truth is that most dips -- store-bought or homemade -- already contain bacteria. Double-dipping adds only a few more microbes than the multitude swimming in your salsa to begin with. If you want to keep your germs to yourself, your best bet is to just eat out of your own private bowl.
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We reported in May that toddlers were less likely to develop asthma and eczema if their pacifiers had been shared by their parents.
Researchers followed 184 babies and their moms for three years, testing them for allergies at 18 months and 36 months. Toddlers were 63 percent less likely to have eczema at 18 months if their parents had sucked on their pacifier, and 88 percent less likely to have asthma.