OK, I assume it was a snake based on the way this hawk was acting. He stood right there, grabbing out with his foot once in awhile, and then stepped back waiting.
Why a snake ? First the bird never did try to grab anything with his beak. Basically protecting his face. Next, not once did he spread his wings out in the ‘mantle’ position to cover the prey from above.
He did watch closely, and was very patient.
Eventually he quickly took off, with no prey. Snakes in the marshes here can be deadly. Predators know this and will give them respect.
The number of different situations we can see during any one shoot is always amazing. A few minutes after this we were visiting Great Blue heron nests.