Skin Effect

Is just an interesting and fun thing to think about, which is one of the laws of the universe that we live in, which will never change and which you can use to your advantage sometimes. Just knowing how the laws of the real universe work, is simple but profound and has so many fun implications. Just don't use these laws in a negative way against other humans.

See: Skin Effect Wiki

When a lightning bolt hits a metal cage and you are inside that metal cage (Also called a Faraday cage). The skin effect says that the flow of electricity will only travel along the outside of the cage, as long as it is an AC current or a short pulse of current. So that even if you were touching the inside of the cage you would not feel any of the energy from the lightning bolt, because of the skin effect, as long as the metal wasn't extremely thin. This is the reason why cars are so safe to be in during a thunder storm. And also they use this theory in the design of airplanes which is why they are so safe to be in during a thunderstorm also.

Another form of skin effect is fire (See: How Wild Fires Work). It only travels up hill and never down hill. So never be on top of a hill when there is a fire, you should always try to stay at the lowest and flattest point possible when making your escape, because fire travels uphill almost instantaneously but on flat surfaces it is very slow to spread in any direction. Also fire only burns at the very tip of an alcohol candles wick, which is good because otherwise the whole thing would catch on fire and explode if not for this effect of fire.
By the way when you see flames they are always the gas of the fuel being burned that is on fire.

Different flammable fuels catch fire at different temperatures. It takes a certain amount of heat energy to change any particular material into a gas, and even more heat energy to trigger the reaction with oxygen. The necessary heat level varies depending on the nature of the molecules that make up the fuel. A fuel's piloted ignition temperature is the heat level required to form a gas that will ignite when exposed to a spark. At the unpiloted ignition temperature, which is much higher, the fuel ignites without a spark.
The above quoted from howstuffworks.com

In other words solids and liquids or solids don't burn it is only the gases of that substance that burn. So even in wood the only way for there to be a flame is when the wood is so hot that it becomes a gas and then that gas is what burns, which we see as a flame. But when you see red hot coals, the wood is so hot that it doesn't even need air to keep on burning because it has such a high temperature that it will stay red hot without oxygen and has to cool down to below combustion temperature before it will go out even without oxygen. Which is the reason why if you pour water onto coals that they will go out, but if you put dirt over it then it won't go out. In other words the water doesn't starve the coal of oxygen, instead it conducts away the heat of the coals in order to cool them down into a low enough temperature to burn out.