After his trial and sentencing, the new convict was sent to the prison down state where he was assigned his jail cell. He met his cell mate who seemed quiet and reserved so he kept to himself.
Shortly after "Lights Out" he heard an inmate in another cell shout out, "417". Immediately there was this loud burst of laughter from nearly every inmate in the cell block. A minute or so after the laughter quieted, another inmate yells out, "23" and again the entire cell block roars with laughter, so much, in fact that the laughing didn't stop for five minutes. This went on for an hour or so. Inmates would yell out number, 115, 72, 319, 256 and on and on.
The same thing happened every night; prisoners would yell out numbers and everyone in the cell block would laugh his head off. So after a week, the new prisoner asks his cell mate, "Why is it that every time somebody yells out a number it seems like the whole prison erupts in laughter?"
"That's easy," says his cell mate, "There is only one book of jokes in the prison library, so all of the inmates have memorized the numbers for every one of the jokes in the book. Then, since everybody knows what the numbers are for each joke, the joke teller can save every body a lot of time by just shouting out the number of the joke he wants to tell."
So the new prisoner goes to the library, checks out the book of jokes and spends the next two weeks memorizing every joke and its number. Then when he is ready, he waits for a lights out and the prisoners start yelling out their numbers, 47, 196, 203, 513, and as usual after every number all of the inmates laugh long and hard.
So the new prisoner yells out, "347!" but there's dead silence, zilch, nada, nothing. He turns to his cell mate and says, "What's wrong? I thought 347 was one of the funniest jokes in the whole book. Why didn't anybody laugh?"
His cell mate answers, "Well, some folks can tell a joke, some can't."