Magnets (scary magnets!)
There are few things that scare me. For the most part things aren't scary. I can control them and predict what they'll do. People, on the other hand, are scary to me.But one of the things that do scare me are magnets. You can see them but the magnetic flux drops off with the square of the distance and what doesn't look like it would hurt you most certainly hurt if you got too close to it.Hell, if you swallow a pair of rare earth magnets you could very well die. They can easily get stuck to each other in your gut with a bit of your tissue between them; soon enough you wind up with a bit of necrosis and problems start to crop up... without immediate surgery you can easily die from swallowing magnets.If you ever want to experience this yourself, but in a slightly safer way, see if you can't find an old hard drive (a spinny one, not an SSD) and take it apart. By the voice coil assembly, you'll have a pair of really strong magnets that aren't as likely to really hurt you much beyond pinching you really hard. Afterward, you'll basically have fridge magnets on steroids.I think I need to make a quick video about this. :-)