Jane laughs at a joke once when you tell it.

Fred laughs at a joke twice. Once when you tell it and once with you explain it to him.

Susie laughs at a joke three times. Once when you tell it, once when you explain it to her, and once when she understands it.

Mark laughs at a joke twice. Once when you tell it and once when you explain it to him. He never understands it.

Will laughs at a joke once when you tell it. There's no use trying to explain it to him.