All Hairstreaks will move their hind wings up and down when perched. If you notice, the tails on the hind wings look like eyespots. This 'false head' is believed to attract potential predator's to this part of the body. If attacked, this part of the wings may be torn away to escape.
The plant in the video is Asclepias incarnata ssp pulchra - Showy Swamp Milkweed.