Watch Your Change

Val and I collect spare change in jars like many other people and convert them into Amazon.com funds (no exchange taken out) at the change machine at Wegmans.
We did our annual holiday time coin exchange today and almost made a bad deal. After the machine totals the coins, one of the comments on the screen is to check the catch at the bottom to see what change did not go through the machine.
We had several coins in the catch, and all but one went back into the machine and registered; fortunately, I looked over the change. The one coin we did not send back in? A 1941 Mercury Head dime, which neither Val nor I know how it got into the change piles we made.