Got it! But what is it?

Mouse?
Snake?
Slow worm?
Big worm?
Frog?
Innards?

I'm watching my favourite kestrel hunting in the next field. They have started to harvest the fodder beet and she is following the harvester very closely. She is up and down very frequently, returning each time to her favourite perch in the oak tree.
I had thought she was catching mice but now I think she is just scavenging on the chopped up fauna left behind my the harvester.
2 more images here
I've lightened these images because I think my monitor needs calibrating and is currrently producing images that are too dark. Perhaps you could tell me what my images are like on your monitor?
HANDHELD!!
canon 5d; 400mm; iso200; f/5.6;1/1250"