To help a friend lose weight, I told her that she should switch to lower-fat foods, including skim milk. When she said her family would drink only whole milk, I suggested that she keep their regular container and refill it with skim milk. This worked for quite a while, until her daughter asked one morning whether the milk was okay.

"Sure, it's fine," my friend answered, fearing she had been found out. "Why do you ask?"

The daughter explained, "Well, according to the expiration date, this milk expired two years ago!"