We are mystified at what Diego Costa is doing here. It looks a little bit like he's biting Gareth Barry, but it could simply be open mouth-to-neck contact with no teeth. Perhaps he blew a raspberry. Maybe this was a lick. We just don't know.
Costa got a red card, but not specifically for whatever this is. Barry got a red card moments later. This supports the idea that Costa is a vampire and turned Barry on the pitch.