I noticed this behavior recently. The bees sit on the board. Then they surround one the of the bees (maybe incoming bee, but I never see pollen on her), maybe 3 around one, and start sniffing it. It amost seems they want to smell her butt the most. THey'll smell top of her throrax, but then get to her butt and smell and scratch away. She on the other hand sort of curls her butt under as if trying to sting the landing board. I don't see any agression or animocity in this interplay and it does not seem like grooming. She is not doing a wiggle dance to lead them to nectar source. What the heck is it?