There are some strong acids in your sromach t hat can corrode many metals and cause them to eenter you blood stream.
If they are "small, powerful magnets" they are probably samarium/cobalt.
From a magnet site:
"You are cautioned, however, that ALL permanent magnets are brittle, and generally when allowed to impact each other, or impact metal, they will chip. The fragments produced in this manner can be extremely hazardous. Chips can get in the eyes if proper protection is not being worn."
Another possibility is neodymium/iron/boron.