The usual stuff: replies (includes quotes), bookmarks, collective read time, likes, number of read markers, internal and external links, etc.
I have noticed that pattern with summarized topics too.
That seems to accurately reflect what actually happens with topics, though: a burst of initial activity when the post is made and publicized on BB and then a “long tail” of a few people coming back to the topic, a handful of new people discovering it, etc.
Certainly less people are reading (and subsequently interacting with) post #243 than post #10, don’t you think?
Of course, we won’t click on topics that don’t look interesting to us. However, what’s your reading strategy for clicking on long (50+ post) topics that do – at least based on the title – look strongly interesting to you?