The other day, our topic was about American jokes.
Do you know Americans say lots of jokes while they are talking?
They say jokes and then enjoy the reaction of people. American joke is something that could happen but rather unusual(people wouldn't do that sort of thing usually). Also it shouldn't be too serious (like my mother is dead or something like that).
Japanese people however, take American jokes seriously most of the times and they don't react the way Americans wanted: Japanese people suddenly become silent and at a loss for words when Americans say jokes.
If an American says something that's a bit unusual, just be nice and say to him or her 'Really?'
And then if he or she says 'Just kidding!' , it means it was an American joke. All you have to do is just laugh.
Just make sure to avoid being silent!