Comment by randcraw

I think the metaphor of doorknobs doesn't really capture what it is that motivates people to converse. To my mind's eye, an door that's ajar is more compelling since it provides a glimpse of myriad untold imaginings that may lie within. Ideally, the not-yet-engaged conversant might be tempted to peek behind this door to speak to something personally of interest to them, regardless of what was said by whomever opened it. I think the trick is to suggest several possible openings such that one manages to suck them in.

A topic I find never fails to engage is a recent movie or book, liked or hated. Why so? Did the techniques of the author or director or cast or production resonate or miss the mark? how would they have changed the plot, the actors, the setting, or the ending? How did this story compare to others they liked more? And so on…

There's nothing magic about movies or books, but everyone has opinions about storytelling and usually feels free to discuss it, since involvement and criticism are pretty much the purpose of fiction in the first place. That's one open door that will usually entice a room of strangers to break the silence.