Bottle gentian and bees

The bottle gentian, Gentiana clausa, is a fall-blooming plant; the deep blue flowers provide a welcome splash of color as the summer-blooming plants die back  Also known as closed gentian, the mature flower looks like it is about to open but never does.

I wondered how such a flower was pollinated, and read that it is done by bumblebees, the only pollinators strong enough to force open the flowers. So I started watching. I had assumed that the bees would force the flower open from the top. But from what I observed, the bees clasp the bottom of the flower, facing downward to get pollen from the base. Fascinating!