We don’t even know what the joke is, but when Mr. Boast laughs–” Laura said to Mrs. Boast. / Mrs. Boast was laughing too. “It’s contagious, she said.” (By the Shores of Silver Lake, Chapter 20, “The Night Before Christmas”)
I have been sitting here trying to think of a person – at some time, somewhere – who made me laugh when they laughed, whose laughter was (as Mr. Boast’s supposedly was) contagious. I must be an awfully somber person or hang around with awfully somber friends, because I can’t think of a soul. Not now. Not ever.
I even tried to think of comedians or actors I’ve seen on televison, in person, or in movies. Still nothing. I can’t think of a single time in my whole life when I heard someone laugh and it made me laugh, even though I had no clue “what the joke was.” There are plenty of smiles out there; people whose smile makes me smile. But outright laughter? Nope…

