산낙지 or, san-nak-ji, is probably the scariest thing you'll ever some across in Korea.
It's LIVE octopus.
It's just a very small kind of octopus that was cut into small pieces while still alive and served immediately, usually lightly seasoned with sesame and sesame oil.
Because its so fresh, its still squirming around the plate!
If you're REALLY adventurous, you can even eat them without cutting them up.
For me, I'm a pescatarian, so while I DO eat fish, the thought of eating a still-living thing really really saddens me. Especially because octopi are so smart! It's totally up to you though, and is definitely a once-in-a-lifetime experience.