Subtitles section Play video Print subtitles [♪ INTRO] Let's say your car breaks down in the middle of the desert, or in a howling blizzard. Your phone battery is dead, and you didn't stock up on food and water like you maybe should've. How are you gonna get out of this one? If you find yourself in a survival situation, you're going to have certain priorities: water, not dying of exposure, not being mauled by wild animals, and, you know, getting back to wi-fi as soon as possible so you can watch SciShow. For most folks, food can actually be a lower priority. But there's a lot of bad survival info out there. Some tips seem too good to be true, and they are. Others are ingrained enough to be common knowledge, except they're wrong. So here's a list of 8 survival tips you definitely shouldn't follow, and what to do instead. First up: water. What about all the snow that's piling up in the blizzard? That is made of water. Snow can be safe to eat, especially if it's freshly fallen. While it can collect contaminants as it falls, things like soot from wood fires and coal plants, that generally won't be enough to hurt you. Snow that's already on been the ground for a while is riskier, since it might have accumulated, like, who knows what, pollutants from the road, maybe, you know, you can insert your own yellow snow joke here. But eating snow might be a bad idea for a different reason: It has to melt inside your body, and that uses your body heat. Water has a high heat capacity, because it has pretty strong bonds holding the molecules together. So you need a lot of energy to break those bonds to boil liquid water or melt ice. Energy your body would otherwise be using to keep you warm. Plus, you'd have to eat a lot of snow to get enough water, since piles of snow contain a lot of air. So to keep your body temperature from falling too much, find a way to melt the snow first. But the worst way to do that is to like hold it against your skin to melt it. Don't do that, it's still going to cool you down. If you're in the desert, don't count on cactuses as like secret jugs of fresh spring water. There's a lot of water in there, yeah. But there's also a bunch of noxious chemicals. Cactuses use an unusual type of photosynthesis, called CAM. CAM photosynthesis uses way less water than other kinds, so it's handy in the desert. CAM plants gather CO2 through pores at night and store it in the form of organic acids. Then they can close those pores during the day to minimize water loss, using the stored carbon to get on with the light-dependent parts of photosynthesis. For storage, they mainly use malic acid, which isn't so bad for you. It's in various fruits, although too much can irritate your mouth. But many CAM plants also make oxalic acid. Oxalic acid is toxic, because it binds to calcium, which can mess up your body. It can also build up in your kidneys in the form of calcium oxalate, the stuff kidney stones are made of. In addition to the acids, a lot of cactus flesh contains alkaloids, which are a diverse family of plant chemicals that generally aren't nice to eat and can really affect your body. Cactus juice won't get you high, like it did to Sokka in Avatar: The Last Airbender. But it can make you sick enough to cause puking or diarrhea, which will dehydrate you and make matters worse. Fishhook barrel cactuses and young prickly pear cactuses contain few enough of the unpleasant chemicals to be kind of edible when raw. They still don't taste good, but they'll do in a bind. But you'd better be pretty confident in your botany skills. Bodily fluids are also mostly water, so you might think you can recycle them. Drinking urine might help you survive ever so slightly longer, but it's only safe to do for a day or so. That's because the waste products in your pee are waste for a reason. If you put them back in your body, they'll build up faster than your kidneys can eliminate them. And that can send you into a state similar to kidney failure, with your body unable to process all of the potassium, nitrogen compounds, and calcium you're throwing at it. As for blood… it's sometimes safe to eat in small amounts. In certain places, it's fairly common, but that's more for its protein and iron content than as a source for water. In large amounts, which you'd need to stay hydrated, blood contains more iron than your body can handle, and it becomes toxic. Your body tries to store it in places like your heart and liver, but that can lead to organ failure and death. Plus, you're at risk from bloodborne pathogens. So going full vampire to survive is probably not the best idea. But let's say you've found some water, and now you need a way to get home without GPS. And maybe you've heard that moss always grows on the north sides of trees. This is one of those things that's true in general, but not 100% reliable all of the time. So it's not so useful for navigation. Here in the northern hemisphere, the northern side of a tree will get the least sunlight, thanks to the Earth's tilt. That means the northern side of the tree is most likely to be shady, cool, and damp, all things that moss likes. Mosses are non-vascular plants, which aren't as good at retaining water as other types of plants. They essentially lack the plumbing to transport water inside of them, so they need all the moisture they can get. So if some other situation is creating good conditions on any particular side of a tree, moss can grow there just fine. It's not necessarily pointing north, it's just the nice-for-moss side. You're going to need some shelter too, or at least a way to stay warm. And you might have seen people in old-timey books or shows giving a swig of booze to warm someone up, especially in a blizzard. This one almost seems intuitive, because alcohol brings a flush of warmth to your cheeks. But that is the exact opposite of what you want if you need to stay warm. Alcohol is a vasodilator, meaning it opens up the blood vessels near the surface of your skin, probably by altering your brain's blood vessel controls. That increased blood flow is why you might feel or look flushed when you're drunk. But it also transports warmth towards the surface of your skin, where it can conveniently diffuse away from your body and into the colder air nearby. Thanks, thermodynamics. When your body is trying to stay warm, it actually constricts those blood vessels to try and conserve warmth in your internal organs and your brain, which need to stay at 37 degrees Celcius to keep ticking. Don't undo that hard work. And if you're cold, rubbing yourself to stay warm seems intuitive, the friction generates a bit of warmth. But once frostbite sets in, that is a horrible idea. On a cellular scale, frostbite means ice crystals are starting to form in your tissues. And ice crystals are sharp. They can puncture cell membranes and other cellular structures, not to mention freeze the water those cells were using to live. Rubbing will jostle those sharp chunks of ice around, and cause them to rupture nearby cells. That's going to make things much worse. Also, even though it's painful, it's not good to thaw those frostbitten toes if they're still at risk of refreezing. More ice forming again will do more damage and risk more permanent loss of tissue. Frostbite mostly affects the extremities. If hypothermia actually sets in, meaning the body's core temperature has dropped below 35 degrees, the key is careful, slow reintroduction of warmth. Plunging a victim of hypothermia in a hot tub could cause irregular heart rhythm or even a heart attack. The proper way to treat frostbite and hypothermia is, like, by a doctor, but when that's not possible, caution is best. Try to sit tight, and don't risk doing more harm. Finally, on your way home, it's best if you can avoid being mauled, bitten, or stung by anything. But if you are, be careful what advice you listen to. Like, that one myth that tells you to like, slice open the snakebite and suck out the toxin. The effects of snakebite vary based on the kind of snake and the venom it's packing. Some bites may cause severe tissue damage and internal bleeding, while others are neurotoxins, there's a bunch! Snake venoms are fascinating! So in reality, this so-called “treatment” will increase the risk of the wound getting infected, possibly spread the venom into the victim's bloodstream much faster, and not actually remove very much venom. In other words, don't do it. An article published in the New England Journal of Medicine in 2002 strongly discourages incision and suction for snakebites. Instead, they recommend keeping the wound below the level of the heart, keeping the victim warm, avoiding tourniquets or any kind of restrictive clothing or jewelry, and getting to the hospital as soon as possible. Hospitals can administer antivenom to neutralize the bite. Antivenom is made up of antibodies that are carefully made to bind to the venom and stop it from having effects on your body. Since different snakes make different kinds of venom, one of the main things is to remember as much as you can about what the snake looked like. You don't need to, like, catch the snake and, like, bring it along with you though, that's not gonna help; nobody's gonna like that. And some kinds of antivenom work for multiple kinds of snakes. It depends on the exact cocktail of antibodies. So you're best off leaving the treatment, hey, to professionals, because I don't think you have a venom-binding antibody serum in your back pocket, and if you do, that should be refrigerated! And last but not least, suppose you're stranded on the shore instead of in a forest and got a nasty jellyfish sting. Should you just… pee on it? Besides sounding totally gross and weird, it's not worth it. Pee doesn't work, and it might even make things worse. Jellyfish tentacles contain stinging cells called cnidocytes, which discharge tiny harpoon-like stingers when they touch you, plus the venom. And some of that venom can poke holes in cells or cause all kinds of biological mayhem. But not many of the cnidocytes on a stinging tentacle fire when you first touch it. So the trick is to get it off you without triggering the thousands of others. The myth claims that urine will neutralize those cnidocytes, so they don't go off and sting you. But certain chemical changes can fire off cnidocytes as well as touch.