Brett-

What did they use the "cow magnets" for in a demonstration?

To whom it may also concern-

No, these magnets are not installed to keep cows from straying. They're very powerful but much smaller. When the cows swallow them the magnets remain in one of their four stomachs and collect the rusty nails and other hardware that cows tend to eat which helps prevent them from puncturing part of the stomach or intestine. If you know anyone who also consumes miscellaneous hardware, you should encourage them to swallow a cow magnet.

Charley Noble