When it comes down to a snake vs. frog for bragging rights, one usually ends up as a bump in the belly just like this.
First off, this may be a fairly common European grass snake, but it has taken the uncommon road of trying to swallow its prey backwards. In a "man-to-man" contest sometimes the frog gets away and sometimes the snake has its dinner and won't let go.
Such is the case here as one slithering suspect has what it wants and doesn't dare lose its grip. It's just that the snake is in the awkward position of having to swallow the frog feet-first and it doesn't look easy.
In nature, it's eat or be eaten, and when an animal has to chase down and catch its prey every day or starve you will get scenes like this.
Here's why we root for the hunters of the world.
Somewhere in a box of old VHS videos I have some footage of this exact same exchange between a garter snake and a toad from way back in the early 1990s. It took forever and a day for the garter snake to swallow the toad backwards, and the toad was making an awful racket.
There is really only one point to nature and its behavior in this way: survival. No one cares if a frog or a toad catches and eats every bug on the planet, but as the food chain rises, so does the level of intensity (and size) between the participants.
All I know is that I've caught a lot of big bass using frogs as live bait, and if I could get some video of the strike, I would, and you would see it right here.