"It's not what you look at that matters, it's what you see." Henry David Thoreau, Mark B
This year, I had a mother hive picked out, and on the day I needed to collect the brood to graft, I opened the hive and they came at me, so I moved to the next candidate. That one didn't, so that one got to be the mother. Mean bees are a pain and a liability.
When I open a hive, what I like to see and hear is a bit of a perk up, then an immediate calm down. You should be able to see and hear this. If there is an immediate and sustained loud buzz and a bunch of running around, know where the smoker is located. It comes with experience.