I like sushi. As such, I respect that sushi is supposed to be as fresh as possible, eaten cold, and so on and so forth. Sure, you risk mercury poisoning and tapeworms, but it is not bad in terms of cold, fresh food.
There should, however, be some limits on how fresh seafood should be:
Yes, you just saw a fish twitching with its flesh made into sashimi.
They Actually Eat That?!
Yes. That fish was prepared in a traditional Japanese cooking style called ikizukuri (生き作り）- literally, "made/done alive."
It starts out somewhat like a good lobster dish in the West: A customer selects a live fish (or squid, whatever) from a tank, which is then cut up like...that on the spot. (Wikipedia mentioned something about the fish swimming around in the tank with its flesh cut like that in between courses, but given the next paragraph, I'm taking it with a grain of salt.)
Exactly how alive the fish is when it gets to the table is up for debate. Some sources say that the fish is reacting in the exact same way that a chicken with its head cut off does - that is, it is twitching because of a massive chemical flood that occurs after successfully dying. Others swear that the fish is still breathing. No matter how you slice it (...I'm sorry, I did not even MEAN that one), it is a fresh dish. A very fresh, sadistic dish.
Although not as hot a topic as dog is in Korea, ikizukuri is controversial in Japan. Like in Greek drama, some people over there prefer their fish to be killed off-screen. Good choice.