Is laughter actually contagious?

As per what Ive read on google, laughter is the auditory expression of happiness. Have you ever joined a random conversation and people started laughing around you but you dont know the context of the laugh? In this case, you would laugh in order to match with the other people

But sometimes you see another person laughing and you laugh because of the funniness involved in the voice of their laugh. Such a weird topic right? Lets end the blog at here for today. So yea laughter isn't contagious... in all situations. Or is it?.....