served for British Breakfast

I have not tried it, and have decided mentioning it because probably you don't want to try it either ...

Black Pudding is served in many hotels as part of the British Breakfast.

It is black and usually made of Pigs blood ....

some people did try it and told me that it is nice ... sounds ridiculous ...

from Wikipedia :
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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.

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.