Microwaves don't really heat food itself, they mostly heat the | ELI5

Microwaves don't really heat food itself, they mostly heat the water inside food. But microwaves don't heat the water evenly. It gets heated in little sections, and those hot parts spread heat to all the cold ones. That takes time though. When food snaps but doesn't get hot its because the water in those hot parts started boiling (that's the sound) but it hasn't been long enough for the heat to spread out (that's why its cold). This is why packages say to let the food sit for a few minutes after cooking. Or you can run the microwave a few seconds on and a few seconds off to spread the cooking time out, which is the same exact thing the "power" setting will do.