People over on Reddit are sharing survival tips that, far from saving your life, will actually get you killed. It turns out there are an awful lot of them out there, and probably a few that you have been told throughout your life.

Below are a selection of the best/worst ones. They could end in you being eaten by an alligator at best, and pooping yourself to death in the desert at worst. As ever, we'll jump in if anything needs elaborating.

"If there's a tornado you should leave your home and go shelter under the nearest freeway underpass"

"In 1991, a local news camera crew survived a tornado by sheltering beneath an underpass near El Dorado Lake, Kansas. The footage went viral (as much as anything could go viral in the 90's) and convinced a lot of people that underpasses were the best place to take shelter," user TheMightyGoatMan wrote.

"As it turns out the El Dorado Lake underpass has some unusual structural features that actually offered a bit of protection, and the news crew were extremely lucky with the angle the tornado hit."

You are more likely to be hit by debris while under the overpass, and could be subject to higher wind speeds created by the narrower passage.

"Lightning never strikes twice in the same place."

"If lightning has found a path that it likes to the ground it's extremely likely to strike there multiple times," CatBoyInAMaidOutfit wrote. "That['s] why lightning rods work."

Yep. In fact, the Empire State Building is struck by lightning about 25 times a year, which is "more than once" if our math is correct. It's best to get inside if you can, or at least avoid any obvious paths that lightning could take to the ground. 

Frostbite

"Concerning frostbite, do not rub someone’s frostbitten skin or pour hot water on it to warm them up," wrote kuroi_sny. "Such measures will damage the skin even more severely."

In an ideal scenario, you would rewarm the frostbitten area under medical supervision in a whirlpool bath containing mild antiseptic. Failing that, a bath containing water of 37°C to 39°C (98.6°F to 102.2°F) is recommended, or failing that, using dry blankets or body heat.

You can drink water from a cactus

"Any liquid inside a cactus will be highly acidic and likely to cause nausea and diarrhea, further dehydrating you," aixbelle points out, correctly. There are a few types of cactus, such as prickly pear cactus, that aren't going to cause you diarrhea or worse. Even those can cause diarrhea, nausea, and increased stool volume when prepared properly.

Don't save your water

"If you have water, drink it," Deminla wrote. "Plenty of people have been found dead, with a cache of water they were holding onto. May seem short sighted, but in a true survival situation, long term survival is something to think about once you've covered your short term basis."

Point your thumb at a nuclear explosion

"The idea that in the event of a nuclear attack you should compare your thumb to a mushroom cloud to see if you're a safe distance away, apparently popularized by Vault Boy from the Fallout games," Bhamv wrote. "Nuclear experts have stated that this 'rule of thumb' is worthless, and that it has never appeared in any sort of manual or guideline for nuclear safety."

While it is worthless, physicists at the University of Leicester did look into it for a paper published in an undergraduate journal, and concluded that for smaller blasts the rule could work.

"This investigation showed that if a 15 kiloton nuclear bomb was to detonate, and your thumb extended at an arm’s length just covered the blast, you could survive most negative radiation effects by running laterally to the direction of the wind for a minimum of 1.65 km in half an hour given that you are standing directly upwind to the blast," they wrote in the paper, before adding "having the stem of the mushroom cloud smaller than your thumb may mean that you could be relatively safe, but it is still always a good idea to evacuate anyway."

Running in a zigzag to outrun an alligator

"Alligators don't run for long distances, so this will probably just waste your energy," TchaikenNugget wrote. "They can also climb some fences and trees as well."

First off, it is true that alligators can run, and fast.

"When alligators walk on land, they can move very quickly and are capable of running at speeds of 7.5 to 9 mph for short distances. The speed at which alligators can move makes them potentially dangerous in water and on land," the University of Florida explains. That's slightly faster than the average human. 

However, alligators do not attack like this, and will not emerge onto land or keep running that fast for long. They prefer a quick sneak up and snack to chasing some zig-zagging buffoon. Simply run away in any direction that isn't "into the water" and you should be safe. Only zigzag if you are feeling particularly fancy.