While I was in the Army stationed in Germany we would go out for an evening meal. They served beer in all the restaurants, and guys I knew would dip a finger in their beer and let a drop fall on their napkin.
I saw this several times, and finally asked one of the guys about it.
He explained that he was a Muslim and their religion forbid drinking one drop of alcohol.
He explained that the drop he let drip on his napkin was the drop he wasn't going to drink.