Fugu Sake is sake that is flavoured with the fins of fugu fish which has just been cut up for sashimi.
The fins are roasted, then then put in cups of hot sake, which are often served flaming.
Many westerners don’t like the smell of the fish and sake together.
In addition to getting it in restaurants, you can also buy it in self-heating tins. There is a picture of a fugu fish on the tins, and actually a piece of roasted fin inside with the sake.