Just as dog owners often don’t realize their canine friends are too heavy, they may have a blind spot about another threat. Surprisingly, the lowly penny can become a lethal weapon against dogs—specifically pennies minted after 1982.

Although all pennies are equal in value—one cent, no matter what year it is— their compositions are not. Pennies that were produced between 1962 and 1982 are predominantly copper (95 percent), whereas pennies churned out in 1982 and after are mostly zinc (97.5 percent).

Zinc is an essential mineral but is undesirable in excessive amounts. When pennies meet the acid in a dog’s stomach, the zinc gets released rapidly, which can destroy red blood cells and, in turn, lead to a number of debilitating conditions, including kidney or liver damage.

Certainly no one was thinking about dogs when the U.S. Mint approved the transition from a copper to a zinc penny. But if Abraham Lincoln were alive today, I’m sure he would say, “One score and thirteen years ago, our fathers brought forth on this continent a new penny, conceived in zinc. So, please, keep them out of reach of your dogs.”