Twitter 上的 Infotale:"Cows are fed magnets that stay in their stomach for life to collect metal objects like nails or barbed wire that the cow will occasionally eat, thus preventing the objects
Bovivet Cow Magnet 10 pack - Farmacy
Master Magnetics COW-RUM5CX3BX Cow Magnet, Ultimate Heavy Duty Ru-Master 5, Steel Ring and Ferrite, 0.75" Diameter, 3.375" Length, Black and Silver (Pack of 3) : Amazon.ca: Industrial & Scientific