Why are some people natural comedians who always seem to come up with the perfect joke at the right time – when most of us struggle to remember a single good one?
Memory experts say there are good neurological reasons why our minds go blank when someone says: "Know any good jokes?"
The secret, according to many of the best comedians, is not to rely on your memory but to write down, squirrel away and categorise every single joke or funny remark you think of or come across.
For 30 years Joan Rivers typed all her jokes on to index cards and filed them away under categories ... like "Parents hated me":
She said: "People think it comes so easily. They have no idea that what you're doing is a terrifically difficult thing to do. I prepare like a crazy lady."
You can see her looking through her card files in this clip from the 2010 documentary Joan Rivers: A Piece of Work:
Her daughter Melissa published a selection of the joke cards (pictured above) in a wonderful scrapbook-style book Joan Rivers Confidential: The Unseen Scrapbooks, Joke Cards, Personal Files, and Photos of a Very Funny Woman Who Kept Everything
Fellow comedian Phyllis Diller – known for her rapid-fire string of one-liners – used a similar method to store and categorise her jokes.
She donated her collection of 50,000 index cards to the Smithsonian institute, who crowd-sourced a project to transcribe and digitise the entire archive.
Hanna , a project assistant at the Smithsonian, blogged about scanning thousands of Diller's joke cards so hundreds of volunteers could go online and transcribe the images into searchable text format.
She said: "While most of the joke cards are simply index cards with a joke typed on, others are more complicated. Some cards have strips of paper glued to them with longer jokes on those papers. Some cards have entire letter-size sheets of paper containing long jokes stapled to the cards. Some cards have comic strips, cut from the newspaper, glued to the cards. "
Bob Monkhouse also categorised and colour-coded his jokes, writing them in longhand in accounting books. He kept a "running file" that he could add to whenever he thought of something new. He made the headlines when two of the books were stolen and he offered a reward for their safe return.
Ronald Reagan used index cards to scribble down quotes, jokes, political wisdom and anything that might be handy for future speeches throughout his career. He always carried a few index cards around with him ready for inspiration to strike. You can see examples of some of his cards in The Notes: Ronald Reagan's Private Collection of Stories and Wisdom