ABLE WAS I ERE I SAW ELBA...is not a pun. It is a palindrome. It reads exactly the same backwards as forwards.

'Pun' is a play on words ( using words that have more than one meaning for example) that have a humorous effect, sounds mostly like a joke. They say 'no pun intended' and it means that the person says something without the intention to make a humorous effect or a joke out of it. Some examples of such play on words: . " I used to be twins. My mother has a picture of me when I was two." " What is the difference between a conductor and a teacher? The conductor minds the train and a teacher trains the mind. " "

'Pun' is the last, and therefore most funny line of a joke.