What is the main ingredient of black pudding?

blood

my dad loved it - eurrgh.

https://en.wikipedia.org/wiki/Black_pudding

More specifically, it's pig's blood.

Black pudding or blood pudding is a sausage made by cooking animal blood with a filler until it is thick enough to congeal when cooled. Blood sausage is a more recent North American term for the same as well as a useful term for similar blood-based solid foods around the world.

Pig or cattle blood is most often used; sheep and goat blood are used to a lesser extent. Blood from poultry, horses and other animals are used more rarely. Typical fillers include meat, fat, suet, bread, barley and oatmeal.

https://www.epicurious.com/recipes/food/views/black-pudding-51145600

Not little thin sausages. Big thick ones that you slice and then fry. Often part of the Big Breakfast at small UK cafes - in the north of England, anyway. When raw, it's brownish, but turns black when cooked. A lot nicer than it sounds.

Here in the US it is not blood but sugar.

Editor's note: [from 2007 x-entertainment.com article, no longer online. No other supporting article could be found.]