There are basically two types of trolling.
Here i'll show them both.  
Say there is a forum with a debate about if a virus is living or not.
The "good" troll would say something along the lines of:
"Why don't we look at what makes a thing living or not instead of restating the obvious."
the "bad" troll would say something that would keep the discussion in a stasis. I think that when people ask questions it is trolling, but in the end it can actually help dig deeper where otherwise you would not have delved into the subject. Trolling is a useful and natural human mechanism that can often ask "why". Some just ask a "why" that locks a discussion or starts acrimony. People may not even have the best of intentions of asking why, but you can gain a greater fufillment from one's bad intentions then from silence.