The snake is really and truly eating the frog.
We found him and the unfortunate frog on our hike while visiting Poland. The frog was alive while the snake was slowly pushing it further and further down his mouth. The frog puffed itself to more than usual size and I think that the snake was slowly loosing the battle and the perspective of juicy dinner. Because he was so engrossed in the act, he was not able to move and we could get very close to him. If we wanted, we could have touched him. And then, suddenly, the frog wiggled out of his grasp and escaped. The snake, I am sure genuinely disappointed, likewise slithered away.