Ha Ha!

Ha Ha! is Nelson's catchphrase and distinctive laugh. Nelson says the laugh with the emphasis on the first "Ha," so it sounds like "HA-ha!"

Nelson usually uses the laugh when something bad happens to another character. Sometimes, after he uses the laugh, he says why he is laughing at the person. For example, he says, "Haw haw! Your dad's not handy!" to Bart after his ten-speed bike (which Homer had assembled) fell apart while Bart was riding it.

Sometimes, Nelson laughs for so long at a time that his voice gets really tired and croaky.

Reversed
When Nelson laughs at Homer while he (Homer) is having a chili-pepper-induced hallucination, Homer hears the laugh with the emphasis reversed: "Haw-Haw!"

Three "Ha"s
In Bart the General, Nelson's first appearance, he laughs with three "Ha"s, particularly when Bart imagines Nelson as a giant who eventually eats him up, and in The War of the Simpsons he laughs like this to Grampa Simpson.

Four "Ha"s
When Nelson appears as a young Beethoven, his laugh has four "Ha"s and he sings it so that it sounds like the opening notes of Beethoven's Fifth Symphony: "Haw-haw-haw-haaaaaaaw, haw-haw-haw-haaaaaaaw!"

Question
Sometimes, Nelson will start the laugh, and then partway through realize that the joke is actually on him, and the laugh comes out sounding like a question: "Haw-Haw?"

Battle Cry
Nelson uses his laugh as a battle cry when he helps Bart and Lisa defend their box fort from a horde of American Shipping Services deliverypeople.

Canadian
The Canadian Nelson says "Hoo Hoo!"

Irish
The Irish Nelson says "Har Har!"

See-Saw
When Bart jumps on the see-saw and the rubbish bag on the other side lands on him, Nelson says "See-Saw" in the same sort of way as "Haw Haw!.

Facebook
Nelson trips up Facebook founder Mark Zuckerberg in a roller-skating rink. Zuckerberg falls and hurts himself and updates his status on Facebook to "in severe pain". Nelson replies, posting "Haw Haw!"

Hallway
In The Good, the Sad and the Drugly, while Milhouse is getting suspended from school, Nelson signs "Haw Haw" at Milhouse.

Uses by Other Characters
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 * Mrs. Muntz has been known to use the laugh.
 * Cypress Hill member B-Real says "Ha-ha!" when he overhears Marge referring to Bart wetting his pants at the Christmas play.
 * Nelson laughs at a tall man driving a Volkswagen, who turns the tables on him. The man makes Nelson walk down the street with his pants pulled down around his ankles, while everyone in Springfield laughs at him.