When a statement or a
joke amuses you to a point, to an extent which would fill you with warmth and make you grin broadly, but not necessarily laugh. It gets you in a personal place. Perhaps it appeals to nostalgia, or it's simply a
joke that only you find
funny, or particularly resonates with you for no apparent reason.
Bob laughs at something for
ten minutes.
Bill: How can you find it that
funny?
Bob: No idea, it just really tickled my pickle.