I'm sorry to give such a dissappointing appraisal, but I think it's a dog. How high was the grass in that field? The motion of that animal just reminded me of a dog trailing something, smelling the ground, running, going back, picking it up again, continuing on.

Dogs come in many shapes and sizes.

I wish it was a mountain lion and that you took the video in PA. You'd be "the man of the year" in the northeast forum

Maybe it's a black panther??