A man calls a refrigerator repair service.
"My refrigerator isn't working."
"What kind is it?"
"It's a small one."
"Electric, gas or propane?"
"Propane."
"Ah! Then the problem is most likely vapor lock. You don't need a service call, just turn the refrigerator upside down for a few minutes to allow the lock to clear. Then put it back and all should be well."
Second call, a few minutes later, "The least you could have done is to tell me to empty the fridge first!"