1. Video of a behavior I did with my cell phone:
This is the second time I saw this. The first time one colony also did it, I was told perhaps a queen flew away (but how could workers know right away?). Indeed I went back to the hive and saw the queen (a virgin?) 2 days later. For this one, I opened it June 25, 2020 at 17:25. Smoked them and they all did this behavior. I did not find a queen, no eggs/larvae. This was a new colony I made with 4 queen cells. I thought the two which emerged (one on each frame) must have fought and perhaps both died.
However, it is possible that a virgin was on a mating flight. So, next day I went back early morning and I saw a virgin queen with some small mating sign still! (The sign must be from the day before!).
2. You should be able to see a tiny whitish thingy at the very tip of her abdomen.
3. Again. I should have grabbed her to take a better photo. I did test her flying ability — she was able to fly (a laying queen usually can only glide downward).