I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it’s powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Honestly, I feel most things would depending on how far back you go:
If you’ve only known stairs your whole life, a lift would seem like a teleportation device.
If you’ve never even seen a wheel, a car would look like a loud metal monster.
If your whole world has been the one village you grew up in, the Internet is just plain incomprehensible.
If you’re used to making fire with a flint, a simple lighter (especially one without a flint in it) would seem like a magical device already.
Now, I’m not saying you couldn’t explain these concepts to them. People in the past where far less stupid than we often think, they just didn’t have the vast knowledge we currently rely on. But if you where to show these things to them without any context, they’d probably think you’re a witch or something