a man was doubtful over his wife's affair with the stranger, so a day before leaving for a business trip, he kept the bowl full of milk under his bed, & tied a spoon in vertical position from downside of the bed. what he observed if the weight of the bed would increase downward by more than a person over it, the spoon will be dipped in the milk & his doubt will become stiff!!

on returning back from a trip he amazed to see - the milk has become butter!!!