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
The entire advanced mathematics. Go sufficiently far and mundane matrix multiplication will look like daemonic sigils. Write out a moderately complex math proof and you’re essentially commanding inhuman tongue. Then when you convince them that it’s really not devil summon spell you can tell the old era folks, that all these symbols is why the sun rises as fast as it does and moon has phases.