It's the carcass of a goat with the goat split up the back from the tail. Those are the two hind legs in view.
It could very well be that Baldwin just popped.
Nothing else but that fits. He was fucked up beyond help. What was that little thing that had him shoot the 2 most important people making his movie with a gun which he had to know was a real gun, with real bullets and not a prop gun? He did get his wish though: What does it feel like to kill a person?