Two basic ingredients — pool cleaner and brake fluid — make one big eruption of fire. Here's a little explosion that can brighten your day.
You can find any number of demonstrations of it under "chlorine and brake fluid," but what you really need is not pure chlorine but a product generally referred to as pool shock. It's calcium hypochlorite. Meanwhile, the brake fluid should be a type with polyethylene glycol. Mix the two together and nothing happens... at first. The mixture just sits there for about five to 30 seconds, then starts hissing, and then comes the leaping red flame.
Calcium hypochlorite is a molecule that's all about pairs. It's a pair of calcium atoms attached to a two pairings of chlorine and oxygen; it cleans out your pool by cozying up to organic matter and promptly falling to pieces, leaving free chlorine atoms that will rip the hydrogen out of anything near them. The reaction will release a lot of heat, but when it's spread out across a pool full of water, the heat doesn't pose a problem. When it's spread over a small expanse of brake fluid, things go a bit differently.
In studies of the reaction, all the brake fluid is consumed by the fire, but no effort on the part of the researchers can get the brake fluid to ignite on its own. The calcium hypochlorite is ripping the brake fluid apart, grabbing the hydrocarbons in it, and the heat from the reaction is making them ignite. In conclusion, boom.
Although there are plenty of videos of people doing this in glass dishes, or capped bottles, they almost invariably shatter — meaning if you try this, shards of broken glass covered in still-reacting chemicals will come straight for your eyeballs. Personally, my favorite video is the reaction in an open soda bottle, since the bottle creepily melts like the Wicked Witch of the West.