I need to research this. Is it only when it's part of your body? I magnetfish a lot. So have quite a bit of rational understanding. And I used to wear a magnetic ring all the time.

Something I found mildly interesting, in the Netherlands I saw this huge cow facility where they could walk freely. There was this machine they could walk into. The machine would attach itself to the cow, get the milk out, and the cow would get nice food. This way the cows milked themselves whenever they felt like it. They were deemed happy cows.