If you like sushi, chances are you love wasabi.
Wasabi is a hot green condiment made from finely grated Japanese horseradish root that is served with all types of sushi and sashimi. It comes either pre-made in a tube or in a powder to which warm water must be added. When properly prepared, it has the consistency of play-doh, but it should not be eaten like play-doh. It is very hot, much hotter than it's friendly green colour sugests.
Some people like a large dollop of it, while others don't care for it at all. Some people like to mix it with the soy sauce they are going to use for dipping while others prefer the more direct route of putting a dab directly onto whatever they are eating.
Wasabi can also be used as an excellent (though temporary) cure for a stuffy nose.