Well, in my understanding, what seems like free and unforced laughter is actually a sort of social signifier intended to grease the conversational wheels: "I am having a good time, we can continue talking." In the same way, Japanese conversations are marked by constant "aizuchi," little words of agreement and encouragement by the listener. A listener can constantly mutter "yes, quite so" and "now I understand," out of reflex, and then immediately follow up with a scathing rebuttal. Interesting cultural difference. In America, you show attention by being quiet and making eye contact.
