I find it kind of interesting how aggro works in Neverwinter. Basically, when you pass a group of mobs at some distance, there are two stages of aggro. Stage one is the mobs turning to stare at you, which is pretty much a warning that you've come too close and that they've noticed you. If you stay in the same place, they will advance to stage two after a couple of seconds, which means actually going into combat.
When you travel around in a group this can be tricky, as the first person that runs past will make the mobs turn, and then the second person immediately gets aggro because the mobs are already alert. Yet of course it's the second person who gets the full blame for aggroing "unnecessary" mobs. It's been fun to observe this when my guildies, who are newer to the game than me and my pet tank, fall behind and end up pulling. (Usually it's me who does that.)