请大家欣赏下面一段幽默故事: keep feeding him nickels a mother saw her three-year-old son put a nickel in his mouth and swallowed it. she immediately picked him up, turned him upside down and hit him on the back, whereupon he coughed up two dimes. frantically, she called to the father outside. “your son just swallowed a nickel and coughed up tow dimes! what shall i do?” yelled back the father, “keep feeding him nickels!”