You need to check your debuff for poison (green puddle) or gaze (orange cone). You'll also see I or II next to it which tells you if you're on first snake set or second snake set duty. The snakes themselves will gaze from either cardinals or intercardinals when they spawn in two at a time and the second two always spawn directly opposite from the first two. If you're a melee or tank you'll need to pay attention to your assigned flex partner. If your debuff matches that of your flex partner your gaze/kill priority changes from either clockwise starting at N cardinal or counter clockwise starting at NW intercardinal. Make sure you don't greed your gcds too much or you'll probably wipe the group. I assume this question is only about Snakes 1. Hope this helps!